I'd just make a remark that even in the GPL world everything is not as simple as it looks. There are GPL versions with _exceptions_ endorsed by RMS, for example. A long time ago I used to work on a Hobbit scheme compiler for the scm interpreter, which was promoted by RMS and became Guile later. scm had such a GPL-with-exceptions clause by RMS, which was stated clearly incorrectly. I take every chance to boast that I convinced RMS to fix the error in his own GPL version for scm :)