According to http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=692621
rabbitmq-server before the 3.0 release use a non-free license :
$ grep -r 'The Software shall be used for Good, not Evil.' .
./plugins-src/rabbitmq-jsonrpc-channel/priv/www/json.js:The Software shall be used for Good, not Evil.
./plugins-src/erlang-rfc4627-wrapper/erlang-rfc4627-git/test/server_root/htdocs/json.js:The Software shall be used for Good, not Evil.
Fortunately they switched to json2.js recently (which doesn't have this licensing clause).
Also please take a look:
It seems that Douglas Crockford finally relicensed it under a free license.
If only Douglas would do the same for jsmin. :P
rabbitmq-server-3.0.4-1.fc18 has been submitted as an update for Fedora 18.