Simon Tatham's Portable Puzzle Collection is a bundle of 24 open source, cross-platform puzzle games. Many of them will look familiar, like Solo (Sudoku), Mines (Minesweeper), and Guess (Mastermind), others perhaps not, but if you like puzzles you're guaranteed to find something addicing in the collection. Each of the games have multiple difficulty levels, save and load functions, multi-level undo and redo, and a few more features, and each one is available for Windows, Linux, Mac OS X, and Palm OS. As if that weren't impressive enough, every puzzle is a download of less than 100kb.