has clause is compatible license of licence software license Source code available Distribution restricted Derivatives allowed Open source software license GNU GPL v3 GNU GPL v2 OPL v1.0 http://www.gnu.org/licenses/license-list.html, accessed 12 June 2013. Open Public License Version 1.0 OPL v1.0 is not a free software license according to the definition of the GNU Project because it requires sending every published modified version to a specific initial developer.