Titan Attacks,described by some as “a retro shooter on steroid” made its way onto Android via the Humble Bundle folks. Puppy Games created Titan Attacks and Grey Alien Games ported Titan Attacks onto Android.
Here are more specific details from the Puppy Games team.
“Titan Attacks for Android is currently exclusively available right now only from the happening-right-now and nearly-finished Humble Bundle for Android & PC #12. You can’t get it from Google Play! Or indeed anywhere else! To make matters even sweeter, you can pay whatever you want for the game (hint: give generously!) – and you also get the desktop version and a Steam key with it (which you’re free to gift away to a friend if you’ve already got it). If that wasn’t awesome enough – and it really is – you get another 9 brilliant games as well!
Honestly, you lucky buggers have never had it so good. You young ‘uns don’t even know you’re born, grumble, etc.”