This is the free version. If you like it, check back again for updates which will include the ability to customize many different options.
Also, I'm currently developing a multiplayer version as well.
Space Battle was built using the love2d game engine found here: http://love2d.org
Decent app but hard to control
Never got the hang of how to maneuver and play this after many attempts even with instructions. Maybe it's just me. I didn't hate the app. I just didn't like it. Deleting it.