I've shipped three CRM forks under three different licenses, and the license decision has caused me more long-term pain than any code decision I've made.
If you're picking a codebase to fork, or deciding what to release your own under, this post is the cheat sheet I wish I'd had in February.
TL;DR
MIT, Apache 2, BSD: ship whatever you want, attribute correctly, move on
GPL v2/v3: anyone you distribute the binary to gets the source






