I'm well aware and have contributed to OpenTofu project in a small manner. I hope you'll forgive me slightly misspeaking - any version of terraform before that license change is OSS. It is, however, perfectly free to use and most companies I've worked with are hard-pinned on a particular version of terraform and rarely on the bleeding edge.
OpenTofu[0] is the OSS fork though.
[0]: https://github.com/opentofu/opentofu
Disclaimer: involved with OpenTofu