FreeMarker 3 is a resumption of work on the well known FreeMarker template engine by the person who is, to all intents and purposes, the original author -- at least of the core parsing/rendering machinery, which really is, more than anything else, what FreeMarker really is. For a more in-depth history, see here. The only other person to have made a contribution to the codebase of any comparable scale is Attila Szegedi, who has stated that he has no objection to FreeMarker 3 simply being copyright Jonathan Revusky, since it simplifies matters considerably.
To be clear (and since the question is bound to keep arising) the version of FreeMarker that is branded as Apache FreeMarker is a continuation of the FreeMarker 2.3 codebase which was largely finalized in late 2004. This version being maintained and developed (again) by the original author is the most advanced version of FreeMarker available. It is also the continuation of a codebase that was never hosted on Apache.
The FreeMarker 3 code is made available under the MIT license:
Copyright (c) 2020-2023 Jonathan Revusky
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.