Libre vs Gratis

The current term in vogue is ``free and open source software'' (FOSS). The ``free'' portion refers to the idea that is embodied in the GNU Public License (GPL). The ``open source'' portion refers to the idea embodied in the Open Source license. They are not the same.

Richard Stallman wrote the GPL. He tried to make sure that everybody could modify, study, use, and change software

• if you change it you pass on your changes.

To do this he wrote a license that states that if you modify GPL software and

• you distribute the modified software
• then you have to make your changes available

This essentially guarantees that the user of your software has the same rights you have.

When you hear the term free think ``free as in speech'' (libre, frei) rather than ``free as in beer'' (gratis, kostenlos).

Open Source software is an attempt to make the GPL more ``business friendly''. It basically requires you to make the source code available. It is a weaker (in a requirements sense) license than the GPL.