The BSD Projects

FreeBSD: The flagship BSD project with solid academic roots.

DragonFly BSD: Originally a fork of FreeBSD, DragonFly BSD is now a superb BSD with many unique features.

NetBSD: Of the BSD projects, by far the most portable.

OpenBSD: OpenBSD focuses on proactive security and code correctness.

And of course:

TrueOS: Now specifically focused on servers. Sponsored by iXsystems.

Project Trident: Formerly PC-BSD, this desktop version is quite versatile. Also sponsored by iXsystems.

Also of note: