If you google Cave story there is a windows and Mac version of this RPG. You can add on the fix to have some English and Chinese translation. This is a freeware game and Pixel and others have contributed to this game.
Since this is a PSP gaming site I would like to turn you on to a PSP upload:
cavestorypsp - Cave Story PSP
Unfortunately I think it is in Japanese but the website and download gives the instructions in English.
What is freeware? If you so choose, you can donate to the party that wrote it. Disclaimer: I have no involvement with any of the parties and was surprised that this is a freeware game for PSP.