Here are a few resources you can use for a variety of game systems. This list is not comprehensive. See What Sort of Games Are There To Play? for an introduction to tabletop rpgs and different genres.

Art Libraries

• Pre-Made Maps
• http://www.opengameart.org - Graphics, Sound Effects, etc.
• http://rpgmapshare.com - maps
• http://www.game-icons.net/ - online repository providing heaps of cool game related graphics(Creative Commons)
• http://rpgvirtualtabletop.wikidot.com/tokens - tokens (free & paid)

Graphics Tools

Useful graphics tools to create maps, tokens and portraits for your games. See also: Useful links for mapping

• GIMP - opensource 2d graphics software(alternative to Photoshop)
• Blender - opensource 3d graphics software

Mapmaking

• Worldographer Generate or create from scratch world/kingdom maps, city/village maps, and dungeon/battlemat maps.
• Campaign Cartographer 3 software
• Dave's Mapper Online mapmaking tool
• Donjon - Random Generators, including dungeons, towns and worldmaps
• Dundjinni fantasy mapmaking software
• DungeonFog- Vector-based online mapmaker (free & premium) shareable maps & export for Roll20
• DunGen - free and high resolution Dungeon Generator, creates maps at 70px per tile and under 5mb to import directly into Roll20.
• GM Friend - hex-based map maker with subhexes and random generation
• GOZZYS.COM - Random Map Generators for Dungeons, Caves, and Wilderness.
• HexTML - free, online mapmaker with custom tiles and multi-user capability
• itch.io Medieval Fantasy City Generator - dynamic online city map generator
• MapForge - Windows/MacOS mapmaking software
• Maper-RPG - online mapmakingeditor, with options to us uploaded images.
• Mipui - simple and fast grid-based mapper with real-time collaboration
• Pyromancer's Dungeon Painter - Dungeon Painter Online(uses flash), and Dungeon Painter Studio(Steam)
• PyMapper - Mapmaker written in Python (Free, last updated 2016)
• RPG MAP EDITOR II by deepnight - online mapmaker
• Tiamat The Tile Mapper Online mapmaker
• http://rpgvirtualtabletop.wikidot.com/mapping-software - List of various mapping tools

Tokens/Portraits

• Hero Portrait Creator
• Token Creator - by rptools.net
• Token Stamp 2 - online token creator
• 2 Minute Token Editor

Sounds

• http://audacity.sourceforge.net - open source sound recorder/editor
• http://www.freesound.org - sounds
• http://www.pdsounds.org - public domain sounds - sound library
• http://sounddogs.com/ - sound effects
• http://tabletopaudio.com/ - Original, 10 minute ambiences and music-loops for your tabletop role-playing games. These loops are now integrated into the Roll20 Jukebox.

There are also SoundPads which are mixing-boards of ambience sounds and music, which can be Broadcast to your players (independently of Roll20).

Gaming Systems by Genre

This is an incomplete display of different game systems by genre. Includes links to obtain rules or rulebooks online as well as Roll20-specific info if such exist. Games listed here should ideally have a Roll20 Character Sheet available.

Fantasy

• Ars Magica 4th Edition free
• BareBones Fantasy by DWD Studios (not to be confused with the Bare Bones Multiverse)
• Basic Fantasy RPG
• Beacon RPG
• Castles & Crusades
• Dungeons & Dragons on Roll20 - Homepage
  • DnD3.5E on Roll20 - D&D 3.5E System Reference Document
  • D&D 5E on Roll20 - D&D 5E Roll20 Compendium | D&D 5E Basic Rules
• Dungeon World - Character Sheet
• Earthdawn - Earthdawn on Roll20
• Fantasy AGE - Roll20 character sheet
• Pathfinder(1E) - Pathfinder 1E SRD
• Pathfinder Second Edition - Roll20 overview - Homepage
• Open Legend RPG - Open Legend on Roll20

Superhero

• Champions
• City of Mist
• Masks
• Mutants and Masterminds
• Marvel Superheros
• Four Color System free
• Supers RED

Modern / Spy / Military

• Covert Ops by DWD Studios
• d20 Modern - by Wizards of the Coast
• Feng Shui- based on Hong Kong/martial arts movies
• GUMSHOE System - by Pelgrane Press
• Mercenaries, Spies and Private Eyes - Designed by Michael Stackpole.
• Modus Operandi - Espionage RPG webring - The unofficial espionage role playing game website, lists most games in the genre
• Over the Edge - by Atlas Games
• Spycraft20 - by Crafty Games - espionage/adventure
• White Lies by DWD Studios (espionage with "white box" D&D-type rules)
• UltraModern5 (5th Edition) Based on D&D 5E, has classes, gear, and scenarios that fits Espionage, Modern Warfare as well as Cyberpunk/Steampunk/Urban Fantasy

Sci-Fi

• Danger Patrol
• Free Spacer - Roll20 Character Sheet
• Star Frontiers (free remastered edition)
• Starfinder - Roll20 Offical sheet - Starfinder (simple) sheet
• Traveller (editions edited by Marc Miller)
• Traveller (Mongoose Publishing edition, soon to go to 2nd edition)
• Star Wars RPG
  • Star Wars RPG by Fantasy Flight Games - Roll20 character sheet
  • Star Wars D6 (WEG) fan resources - Star Wars D6 on Roll20

Horror

• Call of Cthulhu
• World of Darkness - WoD on Roll20

Generic or Multi-genre

• FATE(Core & Accelerated) - Fate on Roll20
• Fiasco
• GURPS - GURPS on Roll20
• Hero System
• Shadowrun - Shadowrun on Roll20
• Savage Worlds - Roll20 character sheet
• OpenD6 (Contains the free rules for D6 Adventure, D6 Fantasy & D6 Space)
• TinyD6 System used in games for multiple genres like Tiny Dungeons & Tiny Supers

Rules-light

• Risus: The Anything RPG free
• Lasers and Feelings free
• Mini Six: Bare Bones Edition free
• Hero Kids

System Specific Tools

D&D

D&D 3.5e

• Monster Generator
• Random Encounter Generator
• Random NPC Generator

D&D 4E

• D&D 4E character sheet service
• Treasure Generator
• Treasure Index
• Combat Manager
• "Drama" / "Bonus" Cards
• D&D 4E Info Tracker
• http://donjon.bin.sh/4e/ - random generators

D&D 5E

• http://donjon.bin.sh/5e/ - random generators
• https://magicalscrolls.com/ - Online Spellbook

Pathfinder

• http://donjon.bin.sh/pathfinder/ - random generators
• http://pathfinder-treasure-generator.com/ - treasure generator

Traveller 5th-edition

• http://eaglestone.pocketempires.com/ - several utilities including Task Roller and ship conversions to T5.

Star Wars

• Free Miniature Maps
• Hyperspace Traveltime Calculator online, system agnostic
• SW Title Crawl Generator
• Star System & Planet Generator online, system agnostic

Star Wars D6

• Quick NPC Generator downloadable exe
• Ship Price Calculator online

Books

• The Lazy Dungeon Master, by Sly Flourish
• Gamemastering By Brian Jamison 330 pages, free
• Grain Into Gold, A Fantasy World Economy A Simple and Sane Supplement for use with your Fantasy Role-Playing Game

Game Master articles

• The Alexandrian, Game Mastery 101
• Sly Flourish, General RPG Advice & DM Deep Dive
• The Angry GM, RPG Advice with Attitude
• Campaign Mastery,Expert advice on creating and running exceptional campaigns.
• The Complete Hippo Massive collection of articles in Gming by user famoushippopotamus
• Economicon Thoughts about D&D fantasy economy and its implications

Youtube Channels

• How to be a Great Game Master channels
• Take20 GM Tips channels
• Matthew Colville Running the Game 58 video playlist
• Web DM Gamemaster tips focused on D&D5e

See Also

• Useful links for mapping
• Game Resources in the Off-Topic forum archive