I’ve always thought that Adventure Module B3 - Palace of the Silver Princess was a better introductory module than B2 - The Keep on the Borderlands. It actually has a plot and has a lot more GM advice.
The first adventure in the Torg adventure trilogy was actually bundled with the GM’s screen, not the boxed set. The adventure in the boxed set had the problem that if the PCs failed it radically changed the game world - the Earth’s rotation relative to the sun stopped, making most of the planet uninhabitable!
I want to say there were a number of hexcrawl adventures for other fantasy systems besides D&D in the 80s and 90s, but the only one I can think of is Griffin Mountain/Island for Runequest.
The original Technomancer adventure was indeed in GURPS Time Travel Adventures, but it was an Infinity adventure; the PCs were a search & rescue team sent to find a missing first-in scout on a newly-discovered world. It always struck me that the secret of extradimensional travel was on the verge of breaking out at any moment in Technomancer; it could be a good choice for a “natives discover their world is in the Infinite Worlds setting” campaign.
For a world-of-the-week game, I’ve gotten pretty good mileage out of my on-again, off-again campaign using the GURPS rules and the setting of Tri Tac Games’ Fringeworthy. There is a limited (though fairly large) supply of explorers in Fringeworthy, and the nature of extradimensional travel means the ease of getting back to home base can vary quite a bit but explorers always know the native language. There are also some interesting limits on gear thanks to the admittedly very rubber science conceit that electricity-based technology (but not brain activity) is stopped and drained by interdimensional travel; whether those limits are good or bad is a matter of taste.