Some years ago, one of my friends and I got the bright idea to make the "Industrial Family Tree", cataloging all of the side-projects, appearances, etc. of various industrial bands.
Granted, this never escaped the braincrack stage, but that doesn't change the fact that that scene is terribly incestuous. (Go look up Pigface on wikipedia, and you'll get an idea of what a challenge trying to map it all out would be)
But anyhow, here's a fun bit of comparison:
Bill Leeb + Rhys Fulber + Some guest vocalist (such as Sarah McLachlan, Kristy Thirsk, or Leigh Nash) = Delerium
Bill Leeb + Rhys Fulber (and no guest vocalist) = Front Line Assembly (or at least did at one point)