It may date back to 2003 but I stumbled upon it just now. It’s http://secondlife.com – a 3D world owned by it’s members. It may sound like it’s the afterlife because of it’s name but in fact it’s just another virtual world.

One of its interesting characteristics is that money is involved here. US dollars and Linden Dollars. With the real money you can buy Linden Dollars, with witch you can live your life in the secondlife. The idea is simple you pump some real money in secondlife, exchange them in L$ and buy a house, or a property, or even better, build your own business. Promote-it, give away some money or make some money, make new friends, do whatever you want, then return to the real life, if you made some money in the meanwhile, exchange them to real money, and maybe return the next day.
Many things can be also traded in the secondlife market.
Another interesting feature is customizability. The user can customize the surrounding objects by appearance as well as behavior. Behavior can be customized trough php code (the user has a help page to guide him trough valid php coding).
Only trough paid membership one can buy land and houses, but you can make some money and have access to the 3D environment trough a free membership also.
With over 3 million residents and over 1 million active users, this can’t go unnoticed. I suggest you give-it a try and have your feedback in a comment at the bottom of this post.