Buddi is under GNU GPL

See http://buddi.digitalcave.ca/license.jsp
Budget is commercial software
Burn is under GNU GPL

http://sourceforge.net/p/burn-osx/code/HEAD/tree/trunk/burn/gpl.txt
Butter is under MIT license (and fix homepage link)

https://github.com/harukasan/butter/blob/master/LICENSE.md
BZFlag is under GNU LGPL

http://bzflag.org/downloads

> BZFlag is licensed under the LGPL 2.1 and is free to
> use/distribute/modify as long as the terms of the license are
> followed.