[wahern]

FWIW, libevent was originally written by an OpenBSD contributor who wished to write portable programs which could make use of kqueue on BSD and select/poll elsewhere. At the time Linux didn't yet have epoll.

In any event, tmux on OpenBSD also uses libevent as libevent is, naturally, part of the base system. libevent as most people know it was originally a portability fork of OpenBSD's version, similar to the portable versions of tmux, OpenSSH, etc, though unlike those projects core libevent development eventually switched to the portable version and OpenBSD stopped (AFAICT) backporting changes wholesale.