[athms]

The author developed tmux on OpenBSD because that is what he used, but it was never part of the OpenBSD Project. It was a port prior to being included in the base install. This is no different that how FreeBSD includes software in its base install, yet this doesn't make the code part of the FreeBSD Project.

The tmux GitHub repo is the reference implementation. As an example, OpenSSH is developed internally to OpenBSD and the project creates a separate portable version. tmux is the opposite, it is developed independently of OpenBSD and the project maintains its own implementation.

[abcdef123xyz]

You are incorrect, tmux is part of OpenBSD and the OpenBSD CVS tree is the main repository.

Edit: because there is occasionally confusion on this point I recently documented it here: https://github.com/tmux/tmux/wiki/Contributing