Blue Wish Resurrection (click the left button [you'll see] to download)
Company's site - beware, japanese
It's an awesome, completely free Bullet Hell SHUMP. Difficult, but in an awesome way. Good soundtrack, and some unlockables, including a true final boss that I'm willing to bet noone here will be able to even get to legitimately, as you need to beat the rest of the game on hell mode (the hardest difficulty) without using a continue. It even has decent sprite-based graphics, but you'll be so busy dodging bullets you won't really notice :p