Rimvydas Jasinskas has consolidated/restored/updated a large number of papers into share/doc on DragonFly.  I’m not going to link to his large number of commits, but instead point you at the directory where they all went.  There’s a number of design documents in there that date back to 4.4BSD and beyond (and some much newer), which may interest or educate you.  Of special note: The Guide to the Dungeons of Doom, for rogue, or the KAME IPv6 implementation notes.