Here’s a list of the Top 10 MMO Worlds:

1. World of Warcraft – 8.5 million subscribers (released 2004)
2. Habbo Hotel – 7.5 million active users (released 2000)
3. RuneScape – 5 million active users (released 2001)
4. Club Penguin – 4 million active users (released 2006)
5. Webkinz – 3.8 million active users (released 2005)
6. Gaia Online – 2 million active users (released 2003)
7. Guild Wars – 2 million active users (released 2005)
8. Puzzle Pirates – 1.5 million active users (released 2003)
9. Lineage I/II – 1 million subscribers (released 1998)
10. Second Life – 500,000 active users (released 2003)