In 1999/2000 I worked on my own Thief levels using the dromed editor - it was both really fun to work with, and utterly frustrating - in a time before open source engines - there were so many small annoying bugs in the editor that would cause it to crash, so you SAVED often and even learned to version files as it was easy to screw up.

But the geometry that could be created was stunning - from courtyards to cathedrals, levels allowed clever use of light and shadow.

"Terra Nova: Strike Force Centauri" Oh my gosh, I remember that game. I picked it up at a computer swap meet, and it was awesome!

Never played Thief, but I logged a lot of hours in Unreal, 1998. I was (and still am) amazed at how full-featured the software renderer was. I always wished I could peek at the code behind it.

If memory serves, the only thing my 3dfx Voodoo3 could do that software-only mode could not was surface reflections. Maybe something with colored lighting too, it's been a long time. Point is, it was a decent enough substitute for dedicated graphics hardware.

People talk about the graphics, but it was the crescendo and decrescendo of guard sounds/singing/footsteps in Thief that made it one of the most immersive games I’ve ever played.

5-hour interview with Sean Barrett where he also talks about the technical details of the Thief engine:

https://www.youtube.com/watch?v=T1tXepGXDDM

To Thief heads who played I and II and want more of it: play The Black Parade, an enormous mod 7 years in the making that is actually an entire new game.

New gigantic maps full of secrets, style faithful to the original, weird universe, new story with voice acting. https://www.ttlg.com/forums/showthread.php?t=152429

I am not affiliated, just a fan.

It's interesting to see parallel development of certain features in the early 3D era and how they were used. The original Prey by 3D Realms was shown in demos in 1997/98 with portal tech including rotating it in a level prop, so it's interesting and ties into the game fiction instead of being only functional to stitch map areas together. There's likely more examples during that period when licensing an engine was less common.