The Adventures of Rick Rocket released for Linux
As mankind is beginning to venture out into the galaxy, a mysterious alien armada appears and attacks the Earth. Space Command calls on its best pilot, Rick Rocket, to take the controls of the X-01 experimental rocket ship and repel the invaders. Join Rick Rocket on an epic adventure across the Milky Way as he first defends the planet and then pursues the alien fleet. Help Rick discover who the aliens are and why they attacked the Earth!
Unlike most shooters, every mission in this game is different.
more here w/ demo