My mind was blown by how good the world of GURPS Reign of Steel, one of many great worldbooks from David L. Pulver.

Clearly an alternate conception of the Terminator universe, but instead of a single Skynet we get over a dozen demigod AIs who have divided the Earth between them, and each have widely varying attitudes to humanity and plans for what to do with us (all bad). This of course makes for (compared to Terminator) a richer world with more opportunities to move between different regions to keep the campaign interesting with the same characters.

The original GURPS Illuminati was rough, but a fun book of inspiration for wild conspiratorial world-girdling secret society weirdness.

When Kenneth Hite started working for SJ Games, he produced a great collection of well-researched and well-written alternate-history weirdness:

• I find GURPS Cabal to be a masterpiece. If you want World of Darkness but less emo goth and more crossed with Kabalah and Illuminati and multi-planar divine power.
• There’s great value in each of GURPS Alternate Earths and GURPS Alternate Earths 2. A few pages fleshes out each entire rich alternate world history, each one well enough to build an entire campaign.
• He ran a regular column, Suppressed Transmission, in the SJ Games magazine. There is a Suppressed Transmission anthology that is well worth dipping into.

I have a lot of love for the World of Darkness adaptations:

• GURPS: Vampire the Masquerade
• GURPS: Werewolf the Apocalypse
• GURPS: Mage the Ascension

They not only brought a much more coherent game system (the original White Wolf system was famously bad), but also brought that GURPS worldbook rigour to the “research” that went into describing the world, the factions, the story hooks, the background, etc.

Like so many other GURPS worldbooks, I thoroughly enjoyed reading them often but never got into a game using them.