CrystalSpace is a portable modular 3D SDK, including many components for building various applications and games - these are still quite useful for projects that do not involve 3D. CS is still very much in development, so anyone who feels inclined to do so can contribute to the source. There are a number of incomplete components still needing to be finished, and a wide array of possibilities for new contributions; for more information about what is missing and a list of currently known bugs, please visit the Developer's Project page at SourceForge:
In the development version of Crystal Space (1.1) we recently added support for decals. In this screenshot you can see how decals will be used in future versions of PlaneShift for doing shadows under characters and for a targetting effect. Of course you can use decals for many other things (footsteps, bullet holes, ...).