• FreeBSD (based on 4.4BSD-Lite)
  • PicoBSD
  • TnyBSD
  • NanoBSD
  • MiniBSD
  • DragonFlyBSD (a FreeBSD 4.X variant)
  • TrustedBSD
  • PCBSD
  • Midnight BSD
  • DesktopBSD

• OpenBSD
  • MirOS (an OpenBSD variant)

• NetBSD

Reference

• Differentiating Among BSD Distros
• Beyond The Big Three BSDs, BSD Alternatives