Tremulous is a computer game that blends a team-based first-person shooter with elements of realtime strategy. The objective of the game is to annihilate the opposing team. This is achieved by eliminating the opposing players and removing their ability to respawn by destroying their spawn structures.
Galcon is an awesome high-paced multi-player galactic action-strategy game. In the game you send swarms of ships from planet to planet to take over the galaxy. It's like arcade action Risk with planets! Anyone can play, and it only takes 30 seconds to learn. Multi-player network games support up to 12 players with teams, and 15 different single player missions against 7 different computer players are provided.
XPilot is a graphical multi-player maneuvering game with less-exciting graphics, but more speed, tactics, and insults. Some people also use it for UDP network analysis. Over the past eight years of playing and development, tons of features have been added to the game, from basic weapons like shotguns and missiles to more recent ones like phasing devices, invisibility, or hyperjump.
Stratagus is a cross-platform real-time strategy gaming engine. It includes support for playing over the Internet/LAN or playing a computer opponent. The engine is configurable and can be used to create games with a wide range of features specific to your needs. Some games based upon it include Battle of Survival, Wargus, and Battle for Mandicor.
Infon Battle Arena is a networked multiplayer real-time programming game featuring little creatures fighting for food. You upload your Creature Code (written in Lua) to a game server using a telnet Interface. The game server then runs your code. The graphical client can be used to watch running games or replay recorded games.