This also includes tools for “mobile-only” play – dice rollers &c. With the OSR in full swing, and people FINALLY taking advantage of the things the internet has always promised, you can start a pick-up game in 10 minutes.
Special mention goes to the blogger formerly known as Djeryv. His site has enough tools and toys to do all that heavy lifting in 5 minutes.
Online Play Tools
Random.org A (very nearly) true random number generator. Since you can set it to any number range, it can simulate some very odd rolls. Need a D136, starting at 120 and ending at 256? here you go.
The Gametable Project What Gabe (younger brother #2) uses to run his campaigns online, and a favorite of /tg/.
Hamachi is a Virtual Private Network client that lets you create a fairly secure server on which to run games. Works well with Gametable if you’re looking for a fast, easy, slightly insecure solution.
Random Content Generators
Multiple content generators
The Donjon: Fast, clean, and useful. Mostly does maps but has a lot of other stuff
Chris Pounds’ random generators: Generate names, random words, and other useful things when you’re stuck.
Abulafia Random Generators: Scads and scads of random content. Spells, weapon names, oracular pronouncements.. all kinds of shit.
Seventh Sanctum: Another multi-generator page. Lots and lots of name generators.
Serendipity: Almost all names, but has some great descriptive generators as well.
Dungeon Crawl Classics Zero-level PC generator: lots and lots of 0-levels now. Great for hirelings.
Meatshields!: Fast, free hirelings and henchies, loosely using OSRIC and OD&D rules.
Mythril and Mages “Labyrinth Lord Treasure on Demand“. Creates one of each treasure type and exports them in a .pdf.
OSR Conservation Process Some random drippings from the internet.
The archives of the One-page Dungeon Contest (need to stock a hex NOW/generate a location for that treasure map? Go here).
The Castle of the Mad Archmage – Module “WG-13”. It’s a pretty impressive megadungeon, but it needs hacking. Review later, if I manage to run it.
Dungeonographer, Hexographer, Hexmapper Some free mapping software, the former two with paid upgrades. Dungeonographer’s website has several different random generators, as well – not quite up to Djeryv’s standards, but excellent nonetheless.
Tablesmith is more of a general tool, but happens to have a built-in map generator.
Autorealm is another generic mapping tool that has a forum community attached. More focused on dungeons and less on realms, sadly.
The Perry-Castanjeda map archive: Lots and lots and lots of historical maps. Flip it, hex it, and rename a couple things and you’re good. I know one guy who ran a campaign in Belgium for almost 2 years and his players never figured it out.
Dave’s Mapper Generates an instant dungeon from user-contributed geomorphic tiles.
Random Traveller Subsector Generator: Great for building country population maps, as well.
Apolitical’s map generator. Good layout patterns, but requires serious hacking to get it onto a page in usable form (it generates the paths, not the actual rooms, and has its own monster tables)
Dizzy Dragon’s Map Generator (loosely based on Dave’s) has absolutely amazing stocking options and a solid and usable interface. One of the best.
Mythweaver’s: Nominally for 3e, but simple and usable. Be aware that the “large” option really isn’t.
Djeryv’s new site (see above) has a random dungeon generator and stocker..
A Pocketmod sheet for Lab Lord (works pretty well for other “advanced” games)
The Mad Irishman Has basically any sheet ever for any published game. I still use his 2x Character sheets.
The Campaign Wiki An archive of D&D House rules and homebrewing. Incomplete, but nifty
LoN’s BESM wiki Various things for BESM, again from my best friend. Occasionally houses other things.
1D4chan The Wiki of 4chan’s /tg/. Some game dev, some weird memes, some awesome, some r34. If you know what 4chan is, you’re safe, if not, you should probably stay away.. They also produce some of the weirdest free games on the ‘net (everything from anime giant robot simulator running over a reskinned Dark Heresy, to a game about posting on an imageboard, to a game about crappy horror B-movies where you get points for living up to stereotypes.)
The H.P. Lovecraft Historical Society Has some excellent props, fonts, and other goodies
Symbols.com An incredibly useful graphical resource.