Here is the list of services I use on Ubuntu
Freetakserver - Open source server with advanced features like web-ui and rest API developed by the civtak community, one of the most popular servers for public use and updated frequently. Supports SSL ( secure ) and TCP connections.
Taky - A lightweight alternative to Freetakserver, also opensource but with not as much features and updated irregulary. Still a great alternative if you need a simple server with simple setup. Great for feeding in a lot of COT data into it, such as ADSB. Supports running multiple servers on a single VPS. Supports SSL ( secure ) and TCP connections.
Traccar - External opensource gps tracking software not associated with ATAK, great for tracking devices which dont have ATAK support and then combining them with Cale-Torinos TAKCAR php script to feed the data into freetakservers REST API.
Mumble server - A voice communication server which can be combined with ATAK using Hayts mumble PTT plugin The mumble server also comes packaged with freetakserver if you use zerotouch install.
Wireguard server - A VPN server used to establish a secure encrypted tunnel connection between clients and the servers.