I’ve used them in a hobby game I’ve been developing with a lot of insight from http://www.roguebasin.com/index.php?title=Dijkstra_Maps_Visu... To implement things like determining if resources are connected to an in game road network. I’ve also used them extensively for the game’s AI for all sorts of different purposes.
Truly a handy tool to have in a game maker’s belt.
The process is, I randomly place some adjacent rooms, completely surrounded by walls. Then I set up a pathfinder (A*) where the cost of moving through walls is large but finite, and the cost elsewhere is tuned so that long detours can cost more than going through a wall. Then I run the pathfinder between various rooms, and place a door wherever the resulting path went through a wall.
This results in doors situated on "desire paths", so they look more or less like they were intelligently placed. It's also tuneable; you can tweak the costs to either get lots of doors and very convenient paths, or minimal doors while still having every room be reachable.
I've been to several game jams where I see amazing prototypes come up in 24-48 hours where people use free or really cheap $5-$40 asset store assets
https://www.google.com/search?q=unity+assets+for+prototyping
It's arguably one reason why there are a glut of games. Not only do engines like Unity and Unreal make it easy to get started but their asset stores have starter kits for almost any type of game. FPS, 3rd person platformer, racing, tower defense game, 2D platformer, etc there's a kit that you download and just start skinning.
https://assetstore.unity.com/search?q=category%3A90&sc=templ...
As someone else mentioned, the Unity asset store has plenty of assets too - some are free, and many others are reasonably priced. There are plenty of 2D assets available, as well as 3D if that's what you're looking for.
Last time I checked, the TOS/EULA says you can use Unity purchased assets outside of Unity games, too - as long as you download them through the Unity editor. So you could potentially use the art assets you buy there even if you want to write your own game engine from scratch.
You might be able to find what you need here, too: