Pricing of Tryton

I’m Francesco, a student of Politechnika Wroclawska.
I just want to know if Tryton is completely free or if I have to pay something to have specific modules.
I hope that someone will help me. Thanks in advance.

Tryton is a free-software under the GPL-3 license. All modules on the Tryton Foundation site are also under the GPL-3 license.
You can find more information here about the GPL-3.