I just wrote to Mark Nottingham, the author of the Cacheability Engine, to ask if he would reconsider licensing the software under the GPL or Affero GPL:
I'm writing to inquire about the Cacheability Engine. I noticed you restrict the software from modification, however I had to patch it to make it work with more current versions of python. Would you please reconsider releasing this software under the GPL or Affero GPL?
Hopefully he'll go for it. :-) If not, that would be a downer, because it's a great piece of software which could help improve website performance.
Oh well, his mail server (pobox.com) just rejected my email, even though I have a reverse IP A record on a static IP, an SPF record permitting the IP to send mail at my domain, and am not block listed anywhere. Too bad.
This is how the software is licensed:
This software may be freely distributed, but may not be modified in any way.