MMORPG?

I recommend Guild Wars 2, I think it's the most casual one currently. The best part you don't have to place any money on trying the game as the core game is fully free and won't cost a dime and you can level to max and fully explore the core world. If you like it you can upgrade and buy the expansions later.

The Elder Scrolls Online is also another good choice and while it's not free. It's only a one time buy with no subscriptions the core game and even Morrowindexpansion can be bought for around 10 or 20 dollars.