DC Land is a function library built on KallistiOS by Dan Potter, the url is http://dcdev.allusion.net/
DC Land has evolved from the basic things we have needed to do since we started Dreamcast programming. It was used to make both Pong and the 3dengine by GreenGianT. For what its worth, we have cleaned it up and decided to release it.
This version of DC Land offers some common 2d graphics functions to draw pixels, lines, boxes, circles and text. There are also simple control pad and vmu functions, s3m sound support and other things like menus and tile grids. We also have implemented some string and conversion functions that we needed at some point as well.
We have made a set of basic examples to go with DC Land. The dcland_examples.tar.gz archive contains 5 examples, each with their own Makefile, binary and c source code.