I really recommend HyperRogue. It has solid roguelike gameplay (though quite colonial thematically), and it takes place in a world with hyperbolic geometry, a fact which permeates every element of the game and goes way beyond a gimmick—the game’s whole balance is based around it. Just go through the tutorial. You can get the game for free or pay for it if you want the most recent updates.

Built into the special options are ways to explore almost any kind of geometry you want, Euclidean, spherical, hyperbolic, connected, three and four dimensional, etc, if you’re into that kind of thing. It even has minigames that are designed for some of these other geometries

I'm not a big gamer, but I thought I'd mention Chogue:
https://jonathanlessard.net/chogue/

It's Chess + Rogue, and open source.

It's Chess + Rogue, and open source.

Nitpick: Yes, it kinda is, but it uses in a non-free game engine (Unity), so can't get it to run here. Sounds like a great idea though. I imagine you control the king and the other pieces on your team behave somewhat like your pets in Nethack? Does it take place on a normal chess board?

If you've ever played Doom then you gotta try Doom, the Roguelike. It's free / libre.

EDIT: Oh, it's actually mentioned in the article.

I deliberately described it as open source and not FOSS for that reason.

You can move any of your pieces, same as in normal chess. The first map is a standard chess board, but after that it transitions to a procedurally-generated rooms-connected-by-hallways-with-fog-of-war sort of thing, but with a chessboard tiling on the ground. All pieces move the way they normally do (and knights can move through walls). The overarching goal is to hunt down the enemy king, who runs away on the first turn of the first board.

I think the authors also made a counterpart called Rogess, which takes place on a regular chessboard and is more similar to normal chess, but with randomized battle mechanics or something, but I haven't played that one.

EDIT: To clarify, I had nothing to do with the development of the game, just thought it would be relevant to mention.

EDIT2: Does the browser version require non-free software? I'm unclear because I don't recall installing some sort of Unity add-on for my browser, but I might have done it a long time ago and forgotten.

What a lovely article!

Moria [...] remapped movement from the H, J, K, and L keys (so chosen for Rogue because they moved the cursor in the vi text editor) to the numeric keypad.

The vi key bindings were what pulled me towards Nethack initially, but I also enjoy how much depth there is to the comestibles. I played Crawl a bit and it seemed like food was mainly just flesh scraped off corpses whereas Nethack takes it to the next level. Questions about eating in Nethack almost make sense outside the context of the computer game itself:

• Should I eat desert first?
• Why did my dog just eat my cat?
• Can vegans eat jewelry?
• How can I tell if a corpse is safe to eat?
• Can I eat humans and sacrifice them to my god?

Yes, veganism is a thing in Nethack. The guidebook even goes into details like this about plant milk:

Also note that “milky” potions may be a translucent white, but they do not contain milk, so they are compatible with a vegan diet.

I think the authors also made a counterpart called Rogess,

Fantastic!

5. h*g3 (Your pawn scored an excellent hit on the black knight) N*h1 (The black knight swings and hits your rook)

Does the browser version require non-free software? I'm unclear because I don't recall installing some sort of Unity add-on for my browser, but I might have done it a long time ago and forgotten.

Yea, the Unity JavaScript isn't free. Didn't work at first because some extensions blocked stuff but made it work now. Cool idea! Reminds me of this chess variant (playable on normal boards) that adds line of sight.

This, in turn, reminds me of Stealth Chess