Drox Operative is a starship action RPG with warring alien races, fierce space battles, a dynamic, evolving galaxy, and co-op multiplayer for Windows and Mac.
Above taken from the main site.

Video example of single player
Multiplayer

This little gem here is something I like to call reactive diablo in space, but is way more than that. The game is like a combination of 4x (explore, expand, exploit, exterminate.) and action rpg. You play the action rpg, explore and exploit parts of the game. You blow stuff up, explore solar systems meeting new races and you exploit them. They offer you missions for money and reputation which you can use for new equipment or to spread rumors/sabotage other races' planets. The races on the other hand, play the 4x part where they must explore, expand, exploit and exterminate each other until one remains. Each sector you create can have random effects too, such as more mobs that do less damage, more shipwrecks for scavanging etc.

As of current patch only one race can be left and you must be allied with said race to win the sector. But they are making it so you can win by getting other races to ally together along with being the last ones standing.

While this game may not have the best graphics, I absolutely love the setting. One game I had 6 races on a medium sized sector who were all nearly allied with each other. But with the help of a few rumors, I spread chaos and destruction throughout the galaxy by making them all go to war with each other, eventually allying with the strongest one to win the sector. Note that this game can get very difficult, I cant even imagine playing on hardcore as of right now.