Sketch is a small, simple system for producing line drawings of
two- or three-dimensional objects and scenes.  It began as a way to
make illustrations for a textbook after we could find no suitable
tool for this purpose.  Existing scene processors emphasized GUIs
and/or photo-realism, both un-useful to us.  We wanted to produce
finely wrought, mathematically-based illustrations with no extraneous
detail.
   
Sketch accepts a tiny scene description language and generates
PSTricks or TikZ/PGF code for LaTeX.  The
sketch language is similar to PSTricks, making it easy
to learn for current PSTricks users.  See
www.pstricks.de for information on PSTricks. 
TikZ/PGF are also very similar except for details of syntax. 
See
http://sourceforge.net/projects/pgf.  One can easily lay raw
PSTricks or TikZ/PGF output over, in, or under
sketch drawings, providing the full power of LaTeX text and
mathematics formatting in a three-dimensional setting.