Does this conworlding software exist?

[alice]

I had a lot of trouble sleeping last night, partly for reasons described elsewhere, but partly because my mind kept fixating on a basic conworlding tool for creating raw heightmaps. This would raise the land under the cursor in response to the left mouse button and lower it with the middle button, so you could draw mountains by dragging the left button much as you would paint strokes in a painting program. Such things do already exist, but they're typically parts of much more extensive programs which you have to pay for or which only run on one operating system. Does anybody know of any simpler and open-source alternatives, or will I have to write the damned thing myself?

[Zju]

Sculptris?
Blender?
No erosion, mind you

[xxx]

I used Terragen a long time ago...

[Vilike]

This sounds like Wilbur, at least what I remember of it. Was still developped recently (2023). Unfortunately, it's Windows-only (haven't tested with Wine yet) and closed-source (but free). (mal)Chances are, you've already tested it

I discovered it at Worldbuilding Pasta, which may contain the exact tool you're looking for somewhere in a post, I don't remember.