One is the historical example of Richard Stallmans own emacs. Another is the wine project (which is notoriously proprietary about stuff making it into the official tree).

In both of these cases the result was forking. The Linux kernel is forked ALL THE TIME by folks with a specific interest that doesn’t coincide with the interests of the powers that be for that project.

This phenomenon is not unique to open source.

The beauty is that with proprietary projects the “fork” must either start from scratch, reverse engineer the original, or steal it (not legal, but not uncommon). Open source makes it easy and legal to do the same things, but conversely amplifies the positive effects of cooperating, and NOT forking.

And every once in a while, the folks behind the fork really do have a better idea how to proceed. See the example of Sodipodi -> Inkscape.