There seems to be such a wide and exciting variety of free MMORPGs (Massive Multiplayer Online Role-Playing Games...what a mouthful!) nowadays. And they keep on rolling in! The latest I've stumbled on is called Hero Online.
This action-packed 3D RPG is similar to Diablo II (to those who are familiar with RPGs). Graphics are extremely colourful and attractive, but seem a bit dated to me (dunno, maybe its just my graphic card). The game comes with a huge amount of quests and subquests to throw your character into. As with what you'd expect with a modern mutliplayer online game, you can fully interact with other characters in your 3D realm - chat, trade, cooperate or challenge them. You also get to tame a pet that grows with you throughout the adventure...kinda cute.
The game is still in beta stage, so there's no telling what extra features are still to come. What I've seen so far looks to be quite promising. Download the current beta here.