Second Life is an online game, of sorts, developed by Linden Lab, a company based out of San Francisco.
The game is not easily described in one sentence, but the best I can think of currently is "Do almost anything you want, kinda like an early Snowcrash".
A lofty description, but it's fairly true.
Rather than a single game, think of it as a meta-game where lots of things happen all the time. Really, it's almost its own world, complete with its own rules of physics, land ownership, a robust economy, and social statuses. Aside from the land masses (which can be terraformed freely anyway), the game is 99% user-created. There is very little (if any) pre-made content, ala Everquest. The users literally make and remake the world on a daily basis.
The world, sometimes referred to as "The Grid", is a patchwork array of 65,526 square meters of land, or "Sims". There are currently around 50 Sims, giving the world a current land size of 3,276,800 kilometers, give or take a few.
The Grid is designed as such in order to be as modular as possible. Each Sim is run off of a separate linux box, running server software that calculates everything happening within the Sim. As users cross Sims (they are all interconnected seamlessly to the user), they "hand off" users (called Avatars) to each other as they move on their merry way. this also gives the extra advantage of avoiding system-wide server crashes; if a Sim crashes, it doesn't take the entire world with it. It also allows Linden Labs to add new areas of the world with relative ease, and also wherever they want to on the Grid, allowing entire continents to spring up overnight. Each Sim also runs the Havok engine, allowing for fairly realistic physical modelling of objects and collision detection. It will soon be upgraded to havok 2.0.
Each Sim also runs scripts, coded in the real-time language made just for the game called the Linden Scripting Language. I'm not much of a coder, but it's designed to be very intuitive with a little learning time. Anyone can script up anything they dream of. Current in-world examples include hoverboards, motorcycles, flying starships, UFO's, catapults, trebuchets, guns of all kinds, atomic weaponry, gearworks, a gift card system, a trivia game, doors, cow launchers, even rudimentary artificial life with emergent behavior. If you can dream it, it is probably possible within scripts. All of this is user-created, mind you.
The game also comes with a simple-yet-powerful 3d shape editor. Each basic shape in Second Life is called a "prim". These include cubes, pyramids, cylinders, spheres, and so on. To make objects, one must simply combine the simple shapes into a complex object. Each object can also be stretched, resized, retextured, and hollowed out to get even more shapes for complex objects. As a result, the world is very robust, with things being modelled from 400-foot-tall zombies down to individual salad forks. All user created, mind you. Did I mention that already? :)
Avatars are each person's personal representation in-world. They can be anything from the mundane (a 3d version of yourself) to the fantastic (space alien, dwarf, Sonic the Hedgehog) to the downright ridiculous (10 feet tall, with a 6 inch round head, holding a katana and a rocketpack, with a record player strapped on your hat singing "The Spam Song". Yes, it's possible, I've done it... don't ask)
Avatars buy up land in the Sims, and can build on their land. They are given an amount of money, and a "grant" each week, which is like a paycheck for playing the game. From there you trade and work with other players, forming businesses or doing jobs for them (like an architect), and amass a monetary fortune. The easiest way to make money in the game is to create your own content and sell it. Content creators make fortunes selling custom clothes (which they make by uploading their own textures after making them in Photoshop or Paint Shop Pro), or useful objects (jetpacks, guns, and swords are popular items), or even building services (I make quite a pretty penny designing houses for people). Other business opportunties abound... in-world, I've seen strip clubs, escort services, taxi drivers, hitmen, private investigators, architects, game show hosts, museum curators, and space aliens. And that's in roughly about a week's time of playing.
Combine all the following together, and you have a VERY vibrant world, unlike any I've seen. There have been many in-world events that were entirely unexpected by the game's creators. For instance, there was a world war in the early stages of the game, instigated by some people from World War II Online. They came, they saw, they conquered... and their neighbors fought back. Whole swaths of the game were devoted to gun turrets and army fortifications. The game makers tried ceasing hostilities by building a wall between the two groups, known as The Jessie Wall but the players just knocked down the wall and spraypainted their slogans on it. Eventually, the game creators removed world-wide damage ability, relegating it to a single Sim, called Jessie. Jessie today is very chaotic still, with wargames happening on a daily basis.
Other in-game events included a tax revolt (people walking around picketing the newbie area with chains attached to their legs, protesting a change in the in-game tax code), weddings, a Burning Man competition, and a Halloween building contest. Not to mention all the little things that go on from day to day, without any press coverage.
SL, by rough estimates, has about 2000 people playing on a daily basis that signed up for a subscription. That makes it smaller than its competitors (There and The Sims Online), but is an order of magnitude more creative and robust than the other games. The players make the world from top to bottom, something unheard of (TSO and There severely restrict the creative abilities of the players). The game makers are always in-world (I've chatted to the CEO of the company at least a dozen times as he's floated about... nice guy, very personable... he was the guy that developed the RealVideo format), fixing this and that, and listening to players. The players even own the things they CREATE (something that doesn't exist in ANY online game at all aside from SL... this is a first), allowing people to actually make a profit off of their jobs in the game, if they wanted.
The world is very surreal... it is reminiscent of a cross between the novel Snowcrash with its Metaverse concept and the movie "What Dreams May come" with its afterlife surreality setting.
Subscription rates are a first, too. For ten dollars, you get a lifetime membership to the game. If you want to buy land, you pay an amount of money per month proportional to how much land you own in-game. For instance, for 512 square meters, you pay 5 dollars a month. If you get rid of the land, you stop paying the 5 dollars a month. Simple as that. You can still play, of course, building and scripting and chatting and creating.
As for possible downsides.. the game is broadband ONLY... it eats a ton of bandwidth as you fly around, as it downloads the content of the world on-the-fly... as a side effect, it also needs rather steep computer requirements (a 2.4 ghz with a Radeon 9800 might work okay, maybe... I run it tolerably with a 1.4 ghz and a Radeon 9000... but the game utilizes your entire computer, so the faster the better). Some people might also have troubles wrapping their heads around the "do anything" concept, but it just takes a nudge in the right direction before they go "OH WOW" and jump right in. You can't lose for ten dollars, anyway (no, I'm not affiliated with the company, I'm just a fanboy ;)
SL requires a credit card to play, more for age verification purposes than actual means of payment. You must be 18 years old or older to play, which is a Good Thing, as it keeps the 11-13 year olds out, making the world a much more civil place. As a result, almost anyone in-world would be more than happy to help you out with any questions you might have (My name is Lordfly Digeridoo in the world.. send me a message :)
The website is at http://www.secondlife.com/, and it's a great deal of fun. I was hooked the first hour, and I've played every day since July 21st. I've really only described perhaps 10% of the entire game... you'll honestly have to experience the rest for yourself.
Update, April 20005
It's been a long time since I wrote this article, and since then SL has undergone some huge changes.
Since December of 2003, Second Life has grown over tenfold. It now encompasses more than 700 sims, and has about 26,000 active residents. The company has added a few features, including custom animations (providing you have Poser). Another interesting feature is the inclusion of streamed audio and video into the world -- you can make your own club with your own music stream, or simply pipe in another shoutcast stream. One resident even managed to figure out how to stream in live music -- from his home -- every tuesday. He's also managed to have a jam session with someone from across the United States -- streaming in perfectly onto the grid!
Furthermore, with the newly added video streaming (as of version 1.6), residents can now host movie parties -- one popular example is "MST3K @ Home", a game show where witty participants congregate in an area and watch terrible movies from the 50's.
Probably most interesting are the things going on inside the world itself.
After the writeup, the game became a lot more commercially focused -- mostly due to the coincidental arrival of several currency exchange services. Due to these services, the Second Life economy has a real-world value -- the economy pumps through about $US 500,000 a week in transactions between residents. One person makes about $US 100,000 a year buying and selling land parcels (a rudimentary real estate agent, essentially).
Recently, one of the residents invented a game called Tringo -- basically a cross between Tetris and Bingo. Because he designed it himself, he gets to keep the copyright on it. As a result, a mobile phone development company paid him licensing rights to have his game distributed onto mobile phone platforms. On top of that, the game is so wildly popular in-world that almost one of every three resident-hosted events (out of several hundred) are Tringo events. Needless to say he's made a lot of money off of a hobby :)
SL has also allowed several universities (most recently Harvard) to come in and study, research, and even hold classes in the world.
Residents have also managed to change others' lives for the better. Several charities have sprung up in-world, benefiting everything from troops in Iraq (several hundred dollars for "goodie" bags for the soldiers), to tsunami relief efforts (several thousand dollars), to Heifer International (another several thousand dollars).
One person spent $US 1000 (plus $US 200 in monthly fees) on his own private island, which he built to assist children with Asperger's Syndrome learn to cope with social situations. Another person, a healthcare worker for severaly physically impaired adults, introduced the world to her charges. The result has been dramatic -- the formerly constrained people now have an entire world at their fingertips, letting them fly, talk, chat, and do everything else, without anyone judging them for their handicaps. They even managed to raise enough money for a more powerful computer so they could enjoy the world even more.
The company, Linden Lab, has doubled in size of employees. They made $US 2.5 million in revenue last year, and secured another $8 million in venture capital funding. They have stated that Second Life grows at a rate of %20 per month -- a staggering feat for a small, niche product such as this.
Anyways, that's just what's been going on lately in-world. Hopefully this was edifying. :)
Update, March 2007
the problem with new technologies is that whenever you write about them, your writeup is immediately dated.
Today, Second Life has morphed into something I could never have even thought about.
26,000 active residents? Try 4.5 million signups, over a million active, and climbing at about 50,000 a day.
The economy is making about $US 1,000,000 worth of transactions every day. The world has a GDP in the several hundred millions.
Linden Lab is fast becoming irrelevent. They open-sourced the client, and other companies are coming in to make a mint on getting other companies into SL. Adidas, Warner Bros, CBS, NBC, Fox Atomic, even political candidates are coming into SL thanks to companies like Millions of Us, Rivers Run Red, and Electric Sheep Company. Some of those companies are writing their own clients to get into Second Life.
The grid of land has exploded from 700 sims to well over 5000. Second Life currently simulates an area of land larger than metropolitan Boston.
Machinima and podcasting happen all the time in Second Life (I'm a weekly contributor to Secondcast, the top SL podcast). Over 4000 people make enough real money in Second Life to live off of it.
Including me. Since July I've been working entirely inside Second Life, building stuff for clients. It's working from home to the max.
What's next year going to bring? I couldn't even tell ya, dude. Flying cars, babies on spikes, dogs and cats living together.