There's 2 games I remember playing when I was a kid - Definitely before 2000, may even be as early as about '96. One was a dungeon crawler - unlike most games I look at from that time frame that seem to always have black backgrounds, I remember this one being predominantly white. I expect it would also qualify as a Roguelike, as the game was purely "drop you in a dungeon, go until you die". I remember the first floor being some kind of a cross, you enter from the bottom, right was a room that often had an enemy that I think was called a Carrion Eater or something similar, and left had some sort of room with benches. A Cafeteria maybe? and straight up had the actual entrance to the dungeon. I don't remember ever getting further than about the second floor in this game, but how hard it actually was, I don't know.
EDIT: Also, this game was isometric from a top-down view, it is VERY reminiscent of many of those core roguelikes
The other game was more of a puzzle game. You were spawned outside of a castle that had a moat all the way around it. You were armed with only a slingshot. I feel like you had the ability to freely move in this game, although I can't remember exactly. The goal of the game, at least at the start, was to shoot about a dozen "sparkly hexagons" (I think they were sparkly, maybe just yellow or red, and they might not have been hexagons either... but I dunno). One of the few really interesting things I remember the game doing was you could stand on the drawbridge, shoot the trigger to raise it and get flung across to a location otherwise unreachable. There was also a number of areas that just killed or trapped you, but I don't think that was actually that unusual back then, so... Anyways, I don't think there were even enemies in this game, but I do remember that the game was slightly random - the "sparkly hexagons" were randomly placed among a number of locations throughout the castle.
If anyone knows either of these... geez, that'd be amazing.
PS. Oh right, both of these games were definitely on PC. Good chance it was Windows 98, but maybe it was 95, I didn't really understand much about OSes at that point.