The current release 0.6 is pretty solid, and can be downloaded for freeBSD, Linux, SGI, and NT. See the release notes for more info.
Though intended as a 3D tool, SLander can also be used for image processing applications, providing a powerfull 2D scipting environment - try it and see...
The SLander engine forms the core of the SL debugging system known as Buffy. In combination with Giles (an SL compiler which generates the required debugging info), Buffy allows shaders to be single stepped, and any variable inspected over a surface.