Sickly Purple Death Ray: RPG and mostly map site.A Literate Programmer's Blog: a lot one RPGs, DFRPG, GURPS and worldbuilding.The Rusty Battle Axe not GURPS focused it does have the very well done Comparing GURPS and D&D on Dungeon Design.Lich Van Winkle's Return to Gaming: "Musings on table-top role-playing games today after spending a quarter century away from them.".James Gameblog: a lot about RPGs and related stuff, including a huge archive and links sparse on the GURPS though.Fergerson (YouTube channel) - while on writing advice it does touch on many issues that can (and do) appear in game worlds. Resources for World-Builders serves index for material focused on A Collection of Unmitigated Pedantry blog that covers old fashioned production of cloth, wars, battlefield leftovers and all the questions which a GM has for background.Arcana wiki: Distilling the Real World for Gaming.One Shot Adventures - A collection of adventures for GURPS in a variety of genres, with premade characters and handouts - so GMs can quickly run a session for new players.
Getting started using the GURPS game aid.Chris Normand channel on GURPS Game Aid for Foundry VTT.
Setting Up Foundry VTT For GURPS: Update.Though Foundry VTT itself is commercial this material is free.
Sadly this program is 32-bit and will not run on Catalina or higher.