Anil Dash wrote a pretty awesome story over at his blog called "Forking is a Feature".
"Still, forks have had important consequences. Firefox (earlier Firebird and Phoenix) was originally a fork of Mozilla, the open source browser that had been mired in indecision for half a decade. WordPress was born as a fork of B2, a neglected early blogging tool."
The article is a great read and can help you when debating whether your company should do more with Open Source software.
What is your favorite forked product?