Here is the Nethack server at alt.org, Telnet link,  Java client, Flash client.  Here is a list of most of the ways to die in the game (dates back to 3.1.3).  And here are a lot of Nethack spoilers.
posted by JHarris on Dec 20, 2011 - 38 comments

Twenty years ago today, the gaming world saw the launch of a truly landmark title: Sonic the Hedgehog. Developed as a vehicle for a new Sega mascot, the fluid, vibrant, cheery-tuned wonderland swiftly became the company's flagship product, inspiring over the ensuing decades an increasingly convoluted universe of TV shows, comic books, and dozens of games on a variety of systems (all documented in this frighteningly comprehensive TVTropes portal). And while in recent years the series has turned out more and more mediocre 3D and RPG efforts, the original games remain crown jewels of the 16-bit era. So why not kick off this anniversary by replaying the titles that started it all for free in your browser: Sonic the Hedgehog (1991), Sonic the Hedgehog 2 (1992), Sonic the Hedgehog 3 (1994), Sonic & Knuckles (1994). Or click inside for music, remakes, and other fun stuff! [more inside]
posted by Rhaomi on Jun 23, 2011 - 71 comments

[FlashFridayFilter] Ski Stunt Simulator [more inside]
posted by Aizkolari on May 14, 2010 - 7 comments

Hanafuda (Koi Koi) is a flash game that plays with the hanafuda deck of cards. (As a trivia side note, hanafuda cards were the beginning of Nintendo.) Once you're familiar with the deck, you can play Minhato, a java game that uses the same cards. [more inside]
posted by klangklangston on Apr 16, 2010 - 19 comments

Ms. Pac-Man 2010
posted by Blazecock Pileon on Mar 26, 2010 - 35 comments

Wayfarer is a 3D rogue-like developed using processing by Ben Hemmendinger. [more inside]
posted by juv3nal on May 16, 2009 - 37 comments

In the mood for a light realtime strategy game? Try Breaking the Tower. It's quite a bit like Settlers, but it's more streamlined.
Runs in the browser, requires java
posted by boo_radley on Mar 24, 2009 - 27 comments

Flash Sunday: Particle-based (explosive) sandbox - another fun toy to play with! Besides the classic earth, water, fire, and plants, this version has air pressure-based physics for wind effects. A mesmerizing tinker-toy. (requires java) (previously) (via)
posted by anthill on Jun 2, 2007 - 21 comments

You have spacial skills. Apply them in Building Houses 2, on mathsnet.net. Or freestyle in Building Houses 1. Or at night! Oh and also there's like a hundred more puzzles over there too. Some java required.
posted by cortex on Apr 12, 2007 - 66 comments

Double Wires (flash) Point and click to shoot out grapples or webs. Move to the right to advance your score.
War of the Hell (java) Get the stick figures to climb your rope and then carefully fling them skyward to 'Heaven'.
(Via d_of_i's always unique DOFI-BLOG, creator of Cat Sledding and the mesmerising Sand Sand Sand.) (Third in a continuing series of physics games posts.)
posted by loquacious on Oct 23, 2006 - 13 comments

Fuzetsu Fire bullets by manuevering your pixel as close as possible to the shots fired by the enemy in the center. Requires Java Runtime Environment. (Since there's no sound, here's a sharity blog whose music would provide an excellent soundtrack: Curved Air.) Game via Jay and Good Experience.
posted by klangklangston on Aug 6, 2006 - 12 comments

Tetrod is a jigsaw puzzle and a four-sided domino game mixed together. -- Java puzzle game; choose 3x4, 4x4, 5x4, or 5x5.
posted by Gator on Feb 24, 2006 - 9 comments

Flea Circus! It's just like Lemmings! Only tinier! And faster! And you can only make three moves: Block, ramp, and other ramp! (java)
posted by Gator on Feb 17, 2006 - 11 comments

The Flowering Nose in Slugland adventure game. As a goblin with a flower for a nose, your ultimate goal is to find the lost sprout. Defeat enemies by throwing flowers at them; power up with hearts; teleport from level to level with such esoteric trinkets as donuts and cherries. (Java.)
posted by Gator on Jan 27, 2006 - 15 comments

Sheep and Dogs [Java] Tricky, but not impossible game of sheepherding with Boids-like movements.
posted by Wolfdog on Jan 5, 2006 - 5 comments

War of The Hell. World of Sand. Hell of Sand. Cat Sledging. Java Friday. [via]
posted by empath on Dec 30, 2005 - 19 comments

Game-Oldies.com features a boatload (approximately) of classic games, playable in Java. Lemmings! Duke Nukem! Toejam and Earl! Trampoline Terror! (What?)
posted by Gator on Nov 11, 2005 - 30 comments

Peekaboom! It's not Friday -- then again this isn't flash -- but it sure is fun. Partner with another anonymous player to identify pictures by gradually revealing them. The kicker is that as we play, the system gets smarter -- the goal is to teach computers how to identify photos the same way we can.
posted by o2b on Aug 4, 2005 - 14 comments

The first rule of Internet Scrabble Club is that you make a predictable Fight Club reference in any posts pertaining to it.
posted by armoured-ant on Feb 17, 2005 - 66 comments

Play the classic lemonade stand game. (jave req'd). Or, for more grown-up fun, play BeerStand (no java req'd).
posted by Ufez Jones on Feb 28, 2003 - 14 comments

For all of you who remember Cosmic Encounter, a java version of it has been released. Of course, this happened several years ago, I just forgot about it until now. It's a fun game, if you can find the people to play it with!
posted by starduck on Jun 11, 2000 - 2 comments