Microsoft 3D Movie Maker Source Code
This is interesting at the bottom of the readme file  Jez also offered this interesting BRender anecdote in an email:

  When Sam Littlewood designed BRender, he didn’t write the code. And then document it.  
  The way most things were built at the time.
  First, he wrote the manual.  The full documentation
  That served as the spec.  Then the coding started.