Two homebrew programmers have just released demos for DS and PSP versions of the freeware PC game Cave Story. A previous attempt by Variant Interactive to publish the game commercially has apparently fallen through, though the company has not officially confirmed this. Fortunately for us, dedicated homebrew programmers aren't content to let the masterpiece remain computer-bound.
Ufo_z, working on the PSP incarnation, has received approval from Pixel and has finished coding up through the first boss encounter. Working on the DS game is ravenworks who has taken a slightly different approach and is re-writing the game to fit the DS system's hardware. Both attempts show a lot of promise and run well on the actual systems or an emulator. Download the DS demo and PSP demo.