Cave Story Beta InformationAfter a question about "cave story beta" was posted on Pixel's BBS he released a set of images relating to a 2003 BETA of Cave Story with exception to the last image, which was released in response to a more recent BBS question about concept art. In these images it is notable that Quote was originally named Curly Brace, Balrog was a basic common monster, and Cave Story looked like a different game back then. A request for a release of the BETA was turned down by Pixel as he felt the BETA was too buggy for a release.
Beta music can be found on the beta music downloads page, whilst tracks that weren't used in the final game can be found on the music downloads page under unreleased tracks. Some very early tracks can be found bundled with piyopiyo player.
Footage of the beta can be found here.
Click on a thumbnail below to see the full image.