Fruition Games have released GSS: Generic Space Shooter. Move left, right and shoot to destroy the oncoming aliens. Although it starts out quite sedate, it doesn't take long for the challenge to ramp-up. End of level baddies, different attack patterns, homing bullets and a variety of stages elevate further than its simple visuals may imply.
With an artist on their team and an increased pace this could really turn into something special. Even so, it's worth playing as-is.