I'm a big fan of Geometry Wars (even though I'm rather bad at it) and I love the fast-paced retro arcade action it delivers. This is an attempt at bringing some of that greatness to the browsers via JavaScript and DHTML. The basic gameplay is the same, albeit in a somewhat simpler form. The different enemy types do have unique behaviours like in the real game which is nice, but it seems your weaponry doesn't upgrade.

The page says it's a prototype, so I'm hoping Geoff will put some more work into it as it's already looking pretty good as it is. The animated sprites are made with a CSS sprite technique. I'm thinking a game with graphics like these (mostly simple shapes) could benefit from canvas, but doing it the old-fashioned way does have the benefit of cross-browser support.

The code is available on GitHub but I couldn't figure out what license he's using.