David O'Toole's Xelf common lisp based game engine is one of those projects that just makes me super excited now and then.

It's also live hackable, so you can code things while they're running. But more than that! There's a smalltalk/scratch-like live object interaction system. And it's so cool! Some recent videos, which I highly recommend watching.

Also, dto has a habit of making some pretty out there games, most of them pretty nostalgaic of the DOS/Atari/Arcade eras, eg inv8r, 4x0ng (also 1-3 x0ngs available), skyw0r, and the much more hand drawn looking Cypress (some other games out there, too).

David O'Toole is also friends with my other lisp game hacking friend, David Thompson (of Sly / Chickadee). They ran a Lisp Game Conference last year.

Cool and inspiring stuff!