Considered by many to be one of the defining indie games, this 2004 metroidvania adventure “received widespread critical acclaim for many polished aspects of its design, such as its compelling characters, setting, story, and gameplay”. While the enhanced Cave Story+ has been given away before, the original is available on Windows, Mac, Linux, Android, half the consoles released in the last few decades (including GameCube, PSP, and Megadrive), Amiga, and even some Motorola devices!
Cave Story+ is well worth the money too! One of the most inventive games of its time, and still a shining example of indie development