GPL and LGPL

It's important to understand the key characteristics of these licenses since they're widely used (GPL maybe more than 70% of total free software).

GNU GPL (GNU General Public License^[6] ) :
- All the 4 freedoms (of course :-))
- + One may not redistribute modified software with changes to the licensing terms : every derivative (improved, modified, mixed, etc.) version must remain under the GPL.
- + One may not mix code under GPL with software under uncompatible license (i.e.: proprietary software)
GNU LGPL (GNU Lesser General Public License^[7] )
- Main difference with the GPL : allows mix between software protected by the GNU LGPL and proprietary software.

Both copylefted licenses enforce users rights and the software freedom through a tight legal control.

This is the best way to ensure a live and rich long-lasting free software portfolio.