The zlib License is a permissive free software license which defines the terms under which the zlib and libpng software libraries can be distributed. It is also used by other free software packages, e.g., on SourceForge. The zlib License has been approved by the Free Software Foundation (FSF) as a free software licence, and by the Open Source Initiative (OSI) as an open source license. It is compatible with the GNU General Public License. The license only has the following points to be accounted for: Note that the license does not require source code to be made available.