|Example of random dungeon map
generated by the scripts in Donjon
These scripts offer a wide range of random generation tools for TTRPGs. Some of which offer incredible complexity.
Random Dungeon Generator
My favourite of these is the random dungeon generator. There are variations for generic fantasy, AD&D, d20 Fantasy, Microlite 20, Pathfinder, and the 4th and 5th editions of Dungeons & Dragons.
You set a name (although a randomly generated one is provided), set the level and size of the party, and choose a motif, which flavours the environment and types of encounters. You can also change the style of the map: determining the size of the map, number of entrances, general layout, etc.
The end result is a map, along with a by-room description of the rooms and corridors, with traps, mysterious effects, evocative detsils, notes on entrances, etc. Even better, the msp is hyperlinked so that clicking on a room automatically takes you to its description in the text below.
If you select a game system other than just plain "Fantasy" a series of level-appropriate encounters ranging from easy to potentially deadly are added.
This is an ideal tool for solo play, quick and dirty design, or just getting your hands on a map if you are not confident in your ability to draw one. I have used Donjon generated maps to playtest various systems in the past.
A generic version is available for download. The version for Dungeons and Dragons 5e includes material from Mordenkainen's Tome of Foes and Volo's Guide to Monsters.
If you just need the encounters, random lists of encounters by terrain, climate, and challenge are also available. Ad are generators for treadure hoards, NPCs, magic items, etc.
Random World Generator
Why stop at Dungeons? Donjon provides a random hex map generator that will build a full world complete with a list of castles, towns and ruins. The maps it creates are gorgeous.
Donjon even has a random campaign generator that fills in one of Matt Coleville's campaign planning sheets with random material. Complete with lore, schemes, major threats, and first adventure outputted.
A Wierd Fiction section contains generators for grim fates, otherworldly entities, and alien artifacts, most statted for Call of Cthulhu d2o.
A Science Fiction setting section includes names, star systems, cyberpunk jobs, ancient junk, alien and mutant race, mecha, starship, and time travel mission jobs for any SciFi setting. It also has system-specific star system generators for Star Wars d6 and Traveller, and a random freight job generator for Star Wars d20.
I've Only Scratched the Surface
The details I have put here are only a fraction of what you can do with Donjon, it is a great website for jump-starting your creativity. You really have to play with it fo awhile to get the full picture.