WireViz: Tool for documenting cables, wiring harnesses and connector pinouts
Man this looks great. So much easier than doing a drawing and you can version it in git etc.If you are looking for feature requests :)  Twisted pairs
  Ability to add cable braid to cable sections
  Ability to add heatshrink to connector backshells
  Ability to specify labels

I had a quick look at the code, looks nice and clean, I might have a go at one of the easier ones (like labels) a bit liater this week.edit: formatting