diff --git a/Sources/ExtensionKit/CoreGraphics/CGPoint.swift b/Sources/ExtensionKit/CoreGraphics/CGPoint.swift
new file mode 100644
index 0000000..ff6a753
--- /dev/null
+++ b/Sources/ExtensionKit/CoreGraphics/CGPoint.swift
@@ -0,0 +1,16 @@
+import CoreGraphics
+
+public extension CGPoint {
+    
+    /// Offset point by new x and y
+    /// - Parameters:
+    ///   - x: x
+    ///   - y: y
+    /// - Returns: new point
+    func offseted(x: CGFloat = 0.0, y: CGFloat = 0.0) -> CGPoint {
+        var point = self
+        point.x += x
+        point.y += y
+        return point
+    }
+}
diff --git a/Sources/ExtensionKit/CoreGraphics/CGRect.swift b/Sources/ExtensionKit/CoreGraphics/CGRect.swift
new file mode 100644
index 0000000..6b12379
--- /dev/null
+++ b/Sources/ExtensionKit/CoreGraphics/CGRect.swift
@@ -0,0 +1,64 @@
+import CoreGraphics
+
+public extension CGRect {
+    
+    var topLeft: CGPoint {
+        return origin
+    }
+    
+    var topRight: CGPoint {
+        return CGPoint(x: maxX, y: minY)
+    }
+    
+    var topMiddle: CGPoint {
+        return CGPoint(x: midX, y: minY)
+    }
+    
+    var bottomLeft: CGPoint {
+        return CGPoint(x: minX, y: maxY)
+    }
+    
+    var bottomRight: CGPoint {
+        return CGPoint(x: maxX, y: maxY)
+    }
+    
+    var bottomMiddle: CGPoint {
+        return CGPoint(x: midX, y: maxY)
+    }
+    
+    var leftMiddle: CGPoint {
+        return CGPoint(x: minX, y: midY)
+    }
+    
+    var rightMiddle: CGPoint {
+        return CGPoint(x: maxX, y: midY)
+    }
+    
+    var midX: CGFloat {
+        return (maxX - minX) / 2
+    }
+    
+    var midY: CGFloat {
+        return (maxY - minY) / 2
+    }
+    
+    /// Center taking size into account
+    var center: CGPoint {
+        get {
+            let x = origin.x + size.width / 2
+            let y = origin.y + size.height / 2
+            return CGPoint(x: x, y: y)
+        }
+        set {
+            origin.x = newValue.x - size.width / 2
+            origin.y = newValue.y - size.height / 2
+        }
+    }
+    
+    var sameCenterSquare: CGRect {
+        let maxLength = max(size.width, size.height)
+        var rect = CGRect(x: 0, y: 0, width: maxLength, height: maxLength)
+        rect.center = center
+        return rect
+    }
+}
diff --git a/Sources/ExtensionKit/CoreGraphics/Operators.swift b/Sources/ExtensionKit/CoreGraphics/Operators.swift
new file mode 100644
index 0000000..8288702
--- /dev/null
+++ b/Sources/ExtensionKit/CoreGraphics/Operators.swift
@@ -0,0 +1,17 @@
+import CoreGraphics
+
+public func +(lhs: CGSize, rhs: CGSize) -> CGSize {
+    return CGSize(width: lhs.width + rhs.width, height: lhs.height + rhs.height)
+}
+
+public func -(lhs: CGSize, rhs: CGSize) -> CGSize {
+    return CGSize(width: lhs.width - rhs.width, height: lhs.height - rhs.height)
+}
+
+public func *(lhs: CGSize, rhs: CGFloat) -> CGSize {
+    return CGSize(width: lhs.width * rhs, height: lhs.height * rhs)
+}
+
+public func /(lhs: CGSize, rhs: CGFloat) -> CGSize {
+    return CGSize(width: lhs.width / rhs, height: lhs.height / rhs)
+}
diff --git a/Sources/ExtensionKit/ExtensionKit.swift b/Sources/ExtensionKit/ExtensionKit.swift
deleted file mode 100644
index 1143b2c..0000000
--- a/Sources/ExtensionKit/ExtensionKit.swift
+++ /dev/null
@@ -1,3 +0,0 @@
-struct ExtensionKit {
-    var text = "Hello, World!"
-}
diff --git a/Sources/ExtensionKit/Foundation/Array.swift b/Sources/ExtensionKit/Foundation/Array.swift
new file mode 100644
index 0000000..bfa3d38
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/Array.swift
@@ -0,0 +1,27 @@
+import Foundation
+
+public extension Array where Element: Equatable {
+    
+    /// Removes the given element in the array.
+    ///
+    /// - Parameter element: The element to be removed.
+    /// - Returns: The element got removed, or `nil` if the element doesn't exist.
+    @discardableResult
+    mutating func remove(_ element: Element) -> Element? {
+        if let index = self.firstIndex(of: element) {
+            return self.remove(at: index)
+        }
+        return nil
+    }
+    
+    /// Returns an array where repeating elements of the receiver got removed.
+    var removingRepeatElements: Array<Element> {
+        var arr = Array<Element>()
+        forEach {
+            if !arr.contains($0) {
+                arr.append($0)
+            }
+        }
+        return arr
+    }
+}
diff --git a/Sources/ExtensionKit/Foundation/CFRunLoopTimer.swift b/Sources/ExtensionKit/Foundation/CFRunLoopTimer.swift
new file mode 100644
index 0000000..d7344c0
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/CFRunLoopTimer.swift
@@ -0,0 +1,10 @@
+import Foundation
+
+public extension CFRunLoopTimer {
+    
+    /// Invalidate CFRunLoopTimer
+    func invalidate() {
+        CFRunLoopRemoveTimer(CFRunLoopGetCurrent(), self, .commonModes)
+    }
+    
+}
diff --git a/Sources/ExtensionKit/Foundation/Collection.swift b/Sources/ExtensionKit/Foundation/Collection.swift
new file mode 100644
index 0000000..503193d
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/Collection.swift
@@ -0,0 +1,13 @@
+import Foundation
+
+public extension Collection {
+    
+    /// Safe indexing.
+    /// Returns the element at the specified index iff it is within bounds, otherwise nil.
+    /// ref: https://stackoverflow.com/questions/25329186/safe-bounds-checked-array-lookup-in-swift-through-optional-bindings
+    ///
+    /// - Parameter index: The index used to retrieve a value / an object.
+    subscript (safe index: Index) -> Element? {
+        return indices.contains(index) ? self[index] : nil
+    }
+}
diff --git a/Sources/ExtensionKit/Foundation/Data.swift b/Sources/ExtensionKit/Foundation/Data.swift
new file mode 100644
index 0000000..18aba2a
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/Data.swift
@@ -0,0 +1,11 @@
+import Foundation
+
+public extension Data {
+    /// Returns a string of hex value.
+    var hexString: String {
+        return withUnsafeBytes { (bytes: UnsafeRawBufferPointer) -> String in
+            let buffer = bytes.bindMemory(to: UInt8.self)
+            return buffer.map {String(format: "%02hhx", $0)}.reduce("", { $0 + $1 })
+        }
+    }
+}
diff --git a/Sources/ExtensionKit/Foundation/Date.swift b/Sources/ExtensionKit/Foundation/Date.swift
new file mode 100644
index 0000000..6d77754
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/Date.swift
@@ -0,0 +1,15 @@
+import Foundation
+
+public extension Date {
+    
+    /// Days of the week in Gregorian calendar (Sunday - Saturday)
+    static let days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]
+    
+    /// Current day of the week in Gregorian calendar
+    var day: String {
+        let gregorian = Calendar(identifier: .gregorian)
+        let weekday = gregorian.component(.weekday, from: self)
+        return Date.days[weekday]
+    }
+    
+}
diff --git a/Sources/ExtensionKit/Foundation/FileManager.swift b/Sources/ExtensionKit/Foundation/FileManager.swift
new file mode 100644
index 0000000..ab67477
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/FileManager.swift
@@ -0,0 +1,67 @@
+import Foundation
+
+public extension FileManager {
+    
+    /// Size of file at path
+    ///
+    /// - Parameter path: file path
+    /// - Returns: Size in bytes
+    func fileSize(atPath path: String) -> Int {
+        let attributes = try? attributesOfItem(atPath: path)
+        return (attributes?[FileAttributeKey.size] as? Int) ?? 0
+    }
+    
+    /// Size of folder
+    ///
+    /// - Parameter path: folder path
+    /// - Returns: size in bytes
+    func folderSize(atPath path: String) -> Int {
+        let manager = FileManager.default
+        if manager.fileExists(atPath: path) {
+            do {
+                let childFilesEnumerator = try (manager.subpathsOfDirectory(atPath: path) as NSArray).objectEnumerator()
+                var folderSize = 0
+                while childFilesEnumerator.nextObject() != nil {
+                    if let fileName = childFilesEnumerator.nextObject() as? String,
+                        let url = URL(string: path) {
+                        let fileAbsolutePath = url.appendingPathComponent(fileName).absoluteString
+                        folderSize += self.fileSize(atPath: fileAbsolutePath)
+                    }
+                }
+                return folderSize
+                
+            } catch {
+                dprint(error)
+            }
+        }
+        return 0
+    }
+    
+    
+    /// Size of directory at URL
+    ///
+    /// - Parameter URL: URL
+    /// - Returns: Size in bytes
+    func directorySize(at URL: URL) -> Int {
+        var result = 0
+        let properties = [URLResourceKey.localizedNameKey, URLResourceKey.creationDateKey, URLResourceKey.localizedTypeDescriptionKey]
+        let manager = FileManager.default
+        do {
+            let urls = try manager.contentsOfDirectory(at: URL, includingPropertiesForKeys: properties, options: .skipsHiddenFiles)
+            for fileSystemItem in urls {
+                var directory: ObjCBool = false
+                let path = fileSystemItem.path
+                manager.fileExists(atPath: path, isDirectory: &directory)
+                if directory.boolValue {
+                    result += directorySize(at: fileSystemItem)
+                } else {
+                    result += try manager.attributesOfItem(atPath: path)[FileAttributeKey.size] as! Int
+                }
+            }
+            
+        } catch {
+            dprint("Error: \(error)")
+        }
+        return result
+    }
+}
diff --git a/Sources/ExtensionKit/Foundation/Global.swift b/Sources/ExtensionKit/Foundation/Global.swift
new file mode 100644
index 0000000..10cddf8
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/Global.swift
@@ -0,0 +1,30 @@
+import Foundation
+
+/// AppVersion set in `CFBundleShortVersionString`
+public var appVersion: String {
+    return Bundle.main.infoDictionary?["CFBundleShortVersionString"] as! String
+}
+
+/// Languages set in user defaults key `AppleLanguages`
+public var systemLanguages: [String] {
+    return UserDefaults.standard.stringArray(forKey: "AppleLanguages") ?? []
+}
+
+/// Sleeps the thread
+/// - Parameter duration: in seconds
+public func sleep(duration: TimeInterval) {
+    #if DEBUG
+        Thread.sleep(forTimeInterval: duration)
+    #endif
+}
+
+/// Swift still calls `print()` and/or `debugPrint()` in shipped apps.
+/// We use a method described in onevcat's post (https://onevcat.com/2016/02/swift-performance/)
+/// to optimaze the performance.
+///
+/// - Parameter item: items to print
+public func dprint(_ item: @autoclosure () -> Any) {
+    #if DEBUG
+        print(item())
+    #endif
+}
diff --git a/Sources/ExtensionKit/Foundation/Int.swift b/Sources/ExtensionKit/Foundation/Int.swift
new file mode 100644
index 0000000..c9b0c11
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/Int.swift
@@ -0,0 +1,72 @@
+import Foundation
+
+public extension Int {
+
+    /// Whether self is an odd number
+    var isOdd: Bool {
+        return !isEven
+    }
+
+    /// Whether self is an even number
+    var isEven: Bool {
+        return self % 2 == 0
+    }
+
+    /// Treats 0 as nil
+    var nilIfZero: Int? {
+        if self == 0 { return nil }
+        return self
+    }
+
+    /// Make the number to string
+    var string: String {
+        return String(self)
+    }
+
+    /// Make a range from zero to self
+    var range: CountableRange<Int> {
+        return 0..<self
+    }
+
+    /// Return a number of instances
+    ///
+    /// - Parameter creation: The initialization of the object
+    /// - Returns: An array containing the objects
+    func instances<T>(of creation: @autoclosure () throws -> T) rethrows -> [T] {
+        return try (0 ..< self).map { _ in
+            try creation()
+        }
+    }
+
+    /// Return if `self` is in the given range.
+    ///
+    /// - Parameter range: Target range.
+    /// - Returns: `true` if self is in the range, otherwise `false`.
+    func inRange(_ range: Range<Int>) -> Bool {
+        return range.contains(self)
+    }
+
+
+    // minutes to seconds
+    var minutes: Int {
+        return self * 60
+    }
+
+    // hours to seconds
+    var hours: Int {
+        return (self * 60).minutes
+    }
+
+    var days: Int {
+        return (self * 24).hours
+    }
+
+    var months: Int {
+        return (self * 30).days
+    }
+
+    var years: Int {
+        return (self * 12).months
+    }
+
+}
diff --git a/Sources/ExtensionKit/Foundation/NSObject.swift b/Sources/ExtensionKit/Foundation/NSObject.swift
new file mode 100644
index 0000000..c94709b
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/NSObject.swift
@@ -0,0 +1,31 @@
+import Foundation
+
+public extension NSObject {
+    
+    /// Exchange two implementations of the given selectors, aka method swizzling.
+    ///
+    /// - Parameters:
+    ///   - originalSelector: The original selector.
+    ///   - swizzledSelector: Another selector.
+    class func exchangeImplementations(originalSelector: Selector, swizzledSelector: Selector) {
+        guard
+            let originalMethod = class_getInstanceMethod(self, originalSelector),
+            let swizzledMethod = class_getInstanceMethod(self, swizzledSelector)
+        else {
+            dprint("Error: Unable to exchange method implemenation!!")
+            return
+        }
+        method_exchangeImplementations(originalMethod, swizzledMethod)
+    }
+    
+    /// Return class name.
+    var className: String {
+        return type(of: self).description().components(separatedBy: ".").last ?? ""
+    }
+    
+    /// Print the deinitialization message of self.
+    final func printDeinitMessage() {
+        dprint("Deinit Message: \(className): \(self)")
+    }
+    
+}
diff --git a/Sources/ExtensionKit/Foundation/String.swift b/Sources/ExtensionKit/Foundation/String.swift
new file mode 100644
index 0000000..13095af
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/String.swift
@@ -0,0 +1,80 @@
+import UIKit
+
+public extension String {
+    
+    /// Is valid email
+    var isEmail: Bool {
+        let emailRegax = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}"
+        let emailTest = NSPredicate(format: "SELF MATCHES %@", emailRegax)
+        return emailTest.evaluate(with: self)
+    }
+
+    /// Are numbers 0-9
+    var areNumbers: Bool {
+        let allnumRegex = "^[0-9]*$"
+        let numPredicate = NSPredicate(format: "SELF MATCHES %@", allnumRegex)
+        return numPredicate.evaluate(with: self)
+    }
+    
+    /// Cast to Int
+    var toInt: Int? { Int(self) }
+    
+    /// Cast to Double
+    var toDouble: Double? { Double(self) }
+    
+    /// Trimming ".0"
+    var trimmingZeroDecimal: String {
+        if let double = Double(self), double.truncatingRemainder(dividingBy: 1) == 0 {
+            return String(format: "%.0f", double)
+        }
+        return self
+    }
+    
+    /// Adding "+" at the very beginning.
+    var addingPlusSymbol: String { "+" + self }
+    
+    /// Adding "-" at the very beginning.
+    var addingMinusSymbol: String { "-" + self }
+    
+    /// Returns the CGSize that the string being layout on screen.
+    ///
+    /// - Parameter font: The given font.
+    /// - Returns: The result CGSize.
+    func layoutSize(with font: UIFont) -> CGSize {
+        self.size(withAttributes: [.font: font])
+    }
+
+    /// Cast as Int and add the given value. No changes if casting fails.
+    mutating func advanceNumberValue(step: Int = 1) {
+        if let value = Int(self) {
+            self = String(value.advanced(by: step))
+        }
+    }
+    
+    /// Comparing app versions. Returns `true` if self is `1.1.0` and the given value is `1.2.0`.
+    /// - Parameter aVersion: Another version.
+    /// - Returns: `true`  if the give version is newer than self.
+    func isOldAppVersion(comparedWith aVersion: String) -> Bool {
+        self.compare(aVersion, options: .numeric) == .orderedAscending
+    }
+    
+    var uppercasingFirstLetter: String {
+        prefix(1).uppercased() + dropFirst()
+    }
+    
+    var lowercasingFirstLetter: String {
+        prefix(1).lowercased() + dropFirst()
+    }
+    
+    /// Return `true` if self is empty or only contains white spaces and/or new lines.
+    var isBlank: Bool { isEmpty || trimmingCharacters(in: .whitespacesAndNewlines).isEmpty }
+    
+    /// Return `false` if self is empty or only contains white spaces and/or new lines.
+    var isVisible: Bool { !isBlank }
+    
+    /// Return `nil` if `self.isBlank` is `true`.
+    var nilIfBlank: String? { isBlank ? nil : self }
+    
+    @available(*, deprecated, message: "Use `nilIfBlank` instead.")
+    func treatsVisuallyEmptyAsNil() -> String? { nilIfBlank }
+}
diff --git a/Sources/ExtensionKit/Foundation/Timer.swift b/Sources/ExtensionKit/Foundation/Timer.swift
new file mode 100644
index 0000000..404340b
--- /dev/null
+++ b/Sources/ExtensionKit/Foundation/Timer.swift
@@ -0,0 +1,38 @@
+import Foundation
+
+public extension Timer {
+    
+    /// Schedule closure to run on main run loop after delay
+    ///
+    /// - Parameters:
+    ///   - delay: Delay interval
+    ///   - handler: Closure to run
+    /// - Returns: `CFRunLoopTimer`
+    @discardableResult
+    class func schedule(delay: TimeInterval, handler: @escaping () -> Void) -> CFRunLoopTimer? {
+        let fireDate = delay + CFAbsoluteTimeGetCurrent()
+        let timer = CFRunLoopTimerCreateWithHandler(kCFAllocatorDefault, fireDate, 0, 0, 0) { _ in
+            handler()
+        }
+        CFRunLoopAddTimer(CFRunLoopGetCurrent(), timer, CFRunLoopMode.commonModes)
+        return timer
+    }
+    
+    
+    ///  Schedule closure to run on main run loop and repeat at the interval
+    ///
+    /// - Parameters:
+    ///   - interval: 触发时长，从现在开始经过interval时长后触发第一次
+    ///   - handler: Closure to run
+    /// - Returns: CFRunLoopTimer
+    @discardableResult
+    class func schedule(repeatInterval interval: TimeInterval, handler: @escaping () -> Void) -> CFRunLoopTimer? {
+        let fireDate = interval + CFAbsoluteTimeGetCurrent()
+        let timer = CFRunLoopTimerCreateWithHandler(kCFAllocatorDefault, fireDate, interval, 0, 0) { _ in
+            handler()
+        }
+        CFRunLoopAddTimer(CFRunLoopGetCurrent(), timer, CFRunLoopMode.commonModes)
+        return timer
+    }
+    
+}
diff --git a/Tests/ExtensionKitTests/ExtensionKitTests.swift b/Tests/ExtensionKitTests/ExtensionKitTests.swift
index 8fc4af9..06bfb4a 100644
--- a/Tests/ExtensionKitTests/ExtensionKitTests.swift
+++ b/Tests/ExtensionKitTests/ExtensionKitTests.swift
@@ -6,7 +6,7 @@ final class ExtensionKitTests: XCTestCase {
         // This is an example of a functional test case.
         // Use XCTAssert and related functions to verify your tests produce the correct
         // results.
-        XCTAssertEqual(ExtensionKit().text, "Hello, World!")
+//        XCTAssertEqual(ExtensionKit().text, "Hello, World!")
     }
 
     static var allTests = [