Kingdom of Loathing (KoL) is a satirical browser-based massively-single player RPG. Players assume one of six classes -- Seal Clubber, Turtle Tamer, Pastamancer, Sauceror, Disco Bandit, or Accordion Thief -- and venture forth on a quest to defeat the Naughty Sorceress and free the imprismed (yep) King Ralph XIV.
Although filled with silly pop culture refences and stick-figure artwork, the game nevertheless has a surprising depth and playability. There are several thousand discrete items that can be found through adventuring or purchased with "meat," the in-game currency -- from the lowly snorkel to the mighty plexiglass pith helmet, from a handful of white chocolate chips to the ominous spooky hi mein. Players are allotted a number of turns to spend each day, and can earn more each day by eating and drinking certain things. There is a robust crafting system for foods, booze, armor, weapons, jewelry, and "miscellaneous" (think "wumpus hair shirt"), and more than a hundred skills to collect each time the player completes the quest, ascends, and begins again. The game allows a variety of play styles, from casual to "hardcore" to "Bad Moon," each with its own restrictions, challenges, and in-game leaderboard showing fastest runs.
There is an active chat system with multiple channels, a simple-but-popular PvP system, clans and clan-specific content , an in-game mall supporting a vibrant in-game economy, active community forums (including a real-life convention held annually in Arizona), and new content and items being introduced monthly by the developers.
Best of all, it is entirely free to play.