Paid Memberships Pro 

Copyright (C) 2013 Stranger Studios, LLC and other contributors

Paid Memberships Pro uses the same software license as the current version of WordPress: GPLv2. You can get the text of that license in the license.txt file of your root WordPress directory or online at http://wordpress.org/about/gpl/.

Please read the GPLv2 for full details, but what this means in practice is that you may install this plugin on any site for personal or commercial use. You may redistribute this plugin any way you choose as long as you maintain the GPLv2 license. If you distribute an altered version of this code, we ask that you:

1. Give your software a name other than "Paid Memberships Pro" or "PMPro" to avoid confusion.
2. Notify us of your distributed version so we can potentially promote the distribution if it's a good effort.