Grid Cartographer

I love mapping my video games. In my childhood, I would draw maps of the mazes you'd always get in Sierra point-n-clicks. And when replaying a game, I'd draw its map all over again, just for the fun of it -- even when I still had my old map available. There's something very satisfying about slowly documenting all the twists and turns of an area until you have the full picture. It feels triumphant, even.
Drawing on paper is fun! But you're bound to make mistakes, and trying to correct too many of them will just make the thing a huge mess. That's where Grid Cartographer comes in. It's powerful but simple to use, and does exactly what I want a digital mapper to do. But it's pricey!!!
The high asking price is justified, considering the advanced features this piece of software has -- even though I'll probably never ever use them. The big one is the GameLink feature that lets you automatically track your position on your map as you play certain old-school dungeon crawlers. Grid Cartographer is still actively supported by its dev, too, despite being almost eight years old now, which is a pleasure to see. There are freeware alternatives, like mipui.net or Gridmonger, but they're either lacking in crucial features or are much more difficult to use.
Having said all that, I'm not completely 100% happy with GC. The set of markers feels limited, especially if you're not playing a fantasy title. You can import more markers, but they're not readily available to grab from anywhere -- I only found a few individual ones on the Grid Cartographer wiki. You end up having to draw your own. Also, I wish there was a way to draw a corridor adjacent to an existing corridor without having to re-draw the wall between them every single time. (But you can use the corridor brush to draw the walls first and then just fill them in, which is marginally easier)
And when a game uses anything other than a neat rectangular or hexagonal grid -- it's back to good ol' paper for me ːkleinesː

I really like GC 4. I saw some complaints about the price and saw enough positives to give it a try. Now I believe the cost is worth it for our workflow.
We’re using it for game‑dev. The map tool lets us build the layout and export it for the mini map. Then we export the .obj model it creates into Blender, mainly to raise the wall height. From there we import the model into the game engine for rapid prototyping.
Also its a one time cost! There is a lot of love that was put into this software.

I think this is a great tool for mapping old CRPGs and even has some particularly nice game link features in that regard, but for the purposes of creating your own TTRPG map I'd say it is very decent and can produce nice-looking maps with very little effort, but it is also missing a couple of features.
Most notably, despite scouring the interface and searching online I can't find any way to make circular rooms beyond a certain size, which seems like a big thing to be missing when even free browser-based mapping tools often have that. I think that and lack of variable size options for things like brushes and markers are the main things I'd appreciate in future updates (if there's any more coming).
More markers would also be nice but more options for non-blocky rooms is really the main thing holding this program back in my opinion.
If there is in fact a way to make true circular rooms besides just putting four half-blocks together (which limits them to a specific size) then please let me know.
Edit to add: I have no idea why but it seems to be running horribly on Linux. It's so laggy it's not really functional anymore.

An incredibly useful tool if you like to play old crpg's (you know who you are). Also very hand for designing maps if you make games yourself.

Fantastic mapping tool.

Excellent. Perfectly done. Every detail is thought.

Excellent!