Space Cowboy was good, though it goes by a different name now.
It was free (with an special item shop) and whilst the PvE was rather lame in my opinion, the PvP was incredible.
Basically there were 4 different space vessels to choose from
A-gear - tank
B-gear - burst dps/all rounder
I-gear - fast dps
M-gear - healing/buffs
and there were 2 factions ANI and BCU. Each faction had its own set of maps which were like nodes which went from the home city to a central hub. There were points added to a faction tally for every kill and this led to huge swarms of players randomly deciding it was time to attack the other faction, this more often than not resulted in a retaliatory strike, leading to a huge battle/stand-off in and around the central hub.
Now once a side got a certain amount of points from kills, they would spawn their mothership, which is basically an enormous NPC ship with a huge amount of health, covered in turrets which would appear in enemy territory. If your side destroys the mothership within 2 hours then you all gain access to certain priveledges, such as a special map, increased recovery of health and stats, among other things.
Apart from all that it was a fairly simple game, every ship/gear could only have 2 weapons attached at one time, primary (missiles) and secondary (guns). But it was good because flying as part of a huge fleet made you feel like you were part of something important.