[jkahn]

That's probably not the best example, as Blender was initially closed-source until the creators went bankrupt. http://en.wikipedia.org/wiki/Blender_(software)

[anthonyb]

But it's been open source for 8 years and under active development:

http://en.wikipedia.org/wiki/Blender_(software)#Development

There can't be a huge amount of the original source left, surely?