Netrek is a multi-player battle simulation with a Star Trek theme.
As a player, you captain starships to engage enemy vessels, bomb
armies and invade planets in order to expand your team's space empire.
The ultimate goal is to genocide the enemy race, but the carnage of
battles along the way is ruthlessly fast paced and a lot of fun!

It's a team-oriented game with realtime dogfighting but involving a
lot of ongoing strategy. It costs no money to play, there are no ads,
and it's open source.

WWW: http://www.netrek.org/