In OpenShift, choose a downloaded cartridge, with the following URL : http://cartreflect-claytondev.rhcloud.com/reflect?github=Filirom1/openshift-cartridge-dart
Then create a dart project with a server.dart, and pubspec.yaml at the root.
The cartridge will launch pub install when you push, and dart server.dart to start your application.
New version of dart doesn't work on CentOS 6.4, the used version is 23200: https://code.google.com/p/dart/issues/detail?id=11920