What Alpha World Has Become...
Alpha World was placed online toward the end of June in 1995 and the public immediately started building there. It crashed in August of 1995, loosing the build database (an event known as "the great asteroid strike").
Except for a couple of near misses (crashed, but the database was recovered from backups) since that time, Alpha World has been built in continuously, and the world size has been expanded several times.
Alpha World still exists and people are still building there. It is currently called AW on the worlds list of the "universe" AW (Alpha World in ActiveWorlds).
Alpha World Today
Alpha World is 655 km by 655 km, or 429,025 square kilometers (in miles this is nearly 407 mi by 407 mi, or approximately 165,647 square miles). Here is a map of Alpha World.
Approximately a quarter of a million people have built in Alpha World since the "asteriod strike", and many of the old builds from the early days are still around.
Note, this is a wild guess based on: Over 350,000 citizenships have been issued, however, many people had more than one citizenship lowering the total. Up until the end of January 2002, tourists (non-citizens) could and did build in Alpha World raising the total. I'm also assuming a high percentage of people who visit the AW "universe" and stay for at least a few weeks, end up building something in Alpha World.
Over 155.5 million objects have been placed in Alpha World as of 26-Mar-04.
I don't know of anything else on the Internet that comes close to this in size, number of "authors", or complexity. Usenet comes to mind, but Usenet is not a single "document" the way Alpha World is. Some of the larger and older news oriented web sites (such as ZD-Net) may have a million or more pages, but Alpha World can be traversed by simply walking, you don't have to click on links or type in URLs to see the next thing on the horizon.
Some have called Alpha World a chat room. In my opinion, to do so completely misses what Alpha World and the ActiveWorlds Technology is all about.