has clause is compatible license of Source code available Usage unrestricted Creative Commons GNU Project Free License Type Copyleft GNU GPL v3 GNU GPL v2 Attribution required CC BY-SA 2.0 Allyson Lister CC BY-SA 2.0 is a copyleft free (free by the definition of the GNU Project) license which lets others remix, tweak, and build upon your work even for commercial purposes, as long as they credit you and license their new creations under the identical terms. The GNU Project recommend this license for art, entertainment and educational works, but also recommend that it is not used for software or documentation, since it is tricky as to how exactly this license is compatible with the GNU GPL. Modified from http://www.gnu.org/licenses/license-list.html, accessed 12 June 2013; Modified from http://creativecommons.org/licenses/, accessed 12 June 2013. Creative Commons Attribution-Sharealike 2.0 Generic Distribution with notices