The Null Device
Toy of the day: PuzzleScript is an online (browser-based) game development environment capable of making a wide variety of turn-based puzzle games, ranging from Sokoban (of which the Hello World-esque example one starts with is a variant) to more sophisticated and/or eccentric games.
Games are written in a functional/declarative notation, consisting of rules; for example, the Sokoban rule allowing the player to push a crate is written as:
[ > Player | Crate ] -> [ > Player | > Crate ]
Graphics are deliberately kept simple, with elements being 5x5 blocks of coloured pixels, giving the game a vaguely Atari 2600-esque aesthetic.
There is a gallery of games made by users, each with an animated GIF representing the game's play. Some examples:
Games were originally turn-based (in that nothing happened except when the player moved), but there is an experimental real-time feature. Somebody has already coded a (semi-functional and not particularly exciting) Pac-Man clone.