zerotier-one/LICENSE.txt

ZeroTier One is licensed under the terms of the GNU General Public License
version 3, which are available here:

http://gplv3.fsf.org/

Modification and redistribution of ZeroTier One is permitted in source form.
Binary distribution is permitted provided all copyright notices remain
intact and any modifications to the source code are also distributed.

ZeroTier One may not be embedded into any closed-source application (e.g. via
linking), nor may closed-source derivatives be created, without a separately
negotiated license from ZeroTier Networks LLC. See the terms of the GPLv3 for
details.