Just started playing a good puzzle-type game for GNU/Linux (and Windows, and OSX I think) where the goal is to control and manipulate data as it flows from inputs, through nodes, to outputs. In each node you write code in a psuedo-Assembler type language to direct the data. You can even manipulate simple graphics using the language (in theory, I haven't gotten to those puzzles yet, I just got the game a few days ago and haven't really had a chance to dig in). There's spot for user created puzzles that I think are written in Lua, but I've not messed around with it too much. There are also sandboxes with in the game where you can just play around with the language. I've done a few of the project Euler problems with the sandboxes to try them out, it's a pretty nice system in general, particularly for people who are just learning programming concepts I would imagine, but it's still fun and rewarding for experienced programmers. Just wanted to turn some people I thought might be interested onto the game. It gives stats at the end of every puzzle about how efficient your code was, how many lines of code you utilized, how many nodes were used, how many cycles it took to complete, et cetera, maybe if anyone else owns the game we could get some optimization discussion going.