Resources

RPG

Starfinder Monster Builder - I use this all the time to create basic Starfinder NPCs. It implements the rules at the back of Alien Archive to let you pick options from dropdowns and come up with final stats that are balanced against other NPCs. From there, I mess with the details as I see fit. Very useful for that first step. The same site also has generators for encounters, loot, and weapons, but I don't use those as much.

Dungeon Scrawl - a web-based mapping tool with an old-school, hand-drawn look. Quick and flexible, but limited capacity for adding objects.
Deepnight Map Editor - another web-based map-maker, even quicker and simpler than Dungeon Scrawl and makes nicer-looking maps, but bad for indoor ones as walls have to be at least one square thick. You'd be surprised how much difference this makes when setting up lighting in roll20. Great for tunnels and caves and the outdoors though.
Dungeondraft - my current preferred "posh map" software. A desktop application that can be loaded with asset packs to create really nice-looking maps to be exported to your favourite VTT or printed out.

Dyson's Dodecahedron - a massive collection of maps and one-page dungeons.
watabou's generators: villages, islands, medieval fantasy cities, and one page dungeons (more on their itch.io page). These are great automated map creation tools, with plenty of configurable options.