- kqueue is a very powerful event loop similar to epoll [1]
- the FreeBSD ports collection is very simple to use as far as compiling from source goes. I only really prefer Debian's apt-get and Gentoo's emerge
- the FreeBSD Handbook is a very well-maintained text [2]. I freely admit OpenBSD has the best man pages ever written, but the Handbook is good too. Not bleeding-edge talk like the gentoo-wiki or archwiki, just reliable information.
[1] https://www.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2
[2] https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/