CPN Tools comprises three major components: the GUI, the simulator, and Access/CPN.

The CPN Tools GUI is licensed under the GNU General Public License (GPL) version 2 as described here.

The simulator is dual-licensed under the GNU General Public License (GPL) version 2 and a 4-clause BSD license as described here.

Access/CPN is licensed under the GNU Lesser General Public License (LGPL) version 2.1 as described here.

NOTE: This is not legal advise! For you as a user, this means you can use the tool more or less at your leisure. You can use the simulator as parts of your open source (GPL) programs with no restrictions, and you can use it as part of commercial or other closed source programs as long as you give us credit. You can use Access/CPN in your program regardless of whether it is open source or not, but if you make modifications to Access/CPN, you must release them.

We are currently in the process of releasing the source, so for now, we refer to these external blog posts for more information: Open-sourcing CPN Tools, and The Access/CPN Source Released.