Rm2k PNG is a library that converts any PNG file to an 8-bit RPG Maker 2000 / 2003 compatible PNG if less than 256 colors are used.
This library was created so that I could build the rm2kfixwatcher tool, which allows users to work in paint tools they're comfortable in without needing to think about managing their palette manually (until they exceed the max 256 colors that is!).