Wizard101 is a family friendly MMO that released in the year 2008 and it's been going strong ever since!
It's a really fun game i feel like more people should talk about. The main Gameplay focusses around fights of 1-4 Players against 1-4 Enemies, Each have a Deck of cards they draw from every turn to determine which Spells they an cast. Spells usually have a cost of "Pips", which are the Magic-esque Mana system of the game. The System itself is relatively simple, but the emergent Gameplay from it is really fun and more unique than any MMO i can think of! Here are a few Screenshots!