While it's an unofficial guide and a homebrew offering, I think The Comprehensive Guide to Collecting & Crafting is a convenient resource for any DM who finds themselves dealing with a player character all about crafting.
GM ideas are written on top of a matching quality illustration in a similar way to a motivational poster.
The cards are system-agnostic, and the starter set provides 200 combinations.
A free online tool that quickly generates a bunch of shops, their inventory, descriptions and stats for everything for sale.
As Dungeons & Dragons, and roleplaying in general, has boomed in recent years so has the demand for custom artwork. Players and DMs are commissioning portraits of characters, hiring cartographers to produce professional maps of homebrew fantasy realms and indie designers invest time looking for illustrators to bring monsters to life.…
The indie TTRPG scene, on the other hand, is brimming with smart, innovative designs based around the mental, emotional, and social lives of individual player characters.
A system to produce randomly designed spacecraft interior maps for tabletop RPGs.
Themed and dynamic encounter tables that can be used for inspiration, flavour or even trigger essential events in your campaign.
If you are looking to GM for the very first time or just looking for a new table top RPG to run, you can try out Mutant: Year Zero using just a free PDF and some spare six-sided dice you scavenge from board games.
Some characters in Black Armada's Last Fleet RPG may be sleeper agents. How does that work?