Plato is offered free under a GNU General Public License (GPL).
When we speak of free software, we are referring to freedom, not price. The GPL is designed to make sure that you have the freedom to distribute copies of free software (and charge for them if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs, and that you know you can do these things.
To protect your rights, we need to prevent others from denying you these rights or asking you to surrender the rights. Therefore, you have certain responsibilities if you distribute copies of the software, or if you modify it: responsibilities to respect the freedom of others.
For example, if you distribute copies of Plato, whether gratis or for a fee, you must pass on to the recipients the same freedoms that you received. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
Plato - Better, Faster Support... Free Copyright (C) 2019, InstantASP Limited Plato is free software: you can redistribute it and/or modify it under the version 3 terms of the GNU General Public License as published by the Free Software Foundation. Plato is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with Plato. If not, see https://www.gnu.org/licenses/ or https://www.gnu.org/licenses/gpl-3.0.txt.
You can find the full GPL version 3.0 license in plain-text format that governs use of Plato here.