intertwingly

In response to Matt, there are lots of Open Source licenses.  I suspect that many of the CC licenses will qualify.  And, yes, Jon Udell recently released some software under a license that some would have you believe was anti-competitive and a cancer.

The key difference between by-sa and GPL is one of marketing genious.

Had Jon merely copyrighted his work, you could have copied it had you asked for and obtained Jon's permission.  All Jon has done is let you know in advance under what conditions you are not even required to ask.

Update: Lawrence Lessig says that CC licenses won't interact with software licenses.  This ignores the fact that they already have.  The most he can say is that his energies are focused elsewhere, which is fair enough.