Epiar

Epiar (ep-ee-are) is an open source computer game, in which the player navigates space from planet to planet, saving money to buy ship upgrades and new ships.

The player can also join mercenary missions, attack other ships to steal their money and technology, and explore the universe. The game combines the action/arcade elements of aircraft dogfighting with the strategy of war games and the openness of role playing games to create this entertaining experience.
Epiar is an open source, open-ended space action/trading game. On the site you can download the full version of the game for free, read the latest news about game development, meet the developers of the game, and even access the source code.