I'm doing a free, open-source operating system for the Nintendo DS. This has been brewing for a few months, and is starting to get ready. Currently FeOS supports loading relocatable code (which includes support for shared libraries), basic console I/O (thanks to libnds' functions), ARM7 code loading support (!!!) and a native libnds-based DS video API.
As usual, it's available through GitHub. Pre-built packages (including the FeOS SDK) will be available soon.
I've also currently ported Lua to FeOS (pictured below), and since there is shared library support, Lua extensions (plugins) are also supported.