there are quite a bit of included stuff that can't be used commercially without privately organising stuff with the artist(s) first.

plenty of other content, namely art, are non-free as well, and not ours to sell (calimer, where are you!)

to really understand what's involved, it's best you read the license.txt files, and the LICENSE files. if one isn't present, assume non-free, and not yours to do with as you please

among restrictive licenses, we have stuff in there that's under the GPL (thank goodness it's just art ). zlib, creative commons (referred to as CC-*) to give you a brief overview