Spelunky by Derek Yu is a 2D side-scrolling roguelike with an emphasis on exploration. You may already be familiar with the more recent Steam, XBLA, and PSN releases of Spelunky, but it originally started as a small, pixel art freeware endeavor made with GameMaker. For the uninitiated, Spelunky is a game about an eponymous spelunker searching for treasure deep in the earth.