GPL 3

The publicly available release on SourceForge is covered by the GNU General Public License Version 3.
Its terms and philisophy are detailed here.

Legalese blurb and disclaimer:

  This program is free software: you can redistribute it and/or modify  
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.