Taisei is a fan-made Open Source clone of the Tōhō series.

It is a shoot ’em up game with lots of bullets (the genre is called bullet hell). It doesn’t aim to rebuild a particular installment of the Tōhō games but is rather an original game set in the world of Tōhō. Enjoy dodging through 6 stages full of new bullet patterns on four difficulty levels.

If you have never played Tōhō before, you can have a look at the manual for an explanation of the controls and game. The game is mostly done and very playable, so feel free to give it a try.