Hello,
Demo version will give you full access to tryton (login/pwd: admin/admin). Then you activate modules you want to test. Otherwise you could use docker image: https://hub.docker.com/r/tryton/tryton/
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
You could check this presentation: An entry-level Tryton presentation