MUDs (specifically Achaea) got me from hunt-and-peck to competent typist. Not even Mario Teaches Typing could manage that.
(never did save up enough to buy wings, though)
I would never have the time for it now that I'm a bit older, but I had a great time and probably played for 6 or 7 years in total.
It's 100% where I learned to code and to coherently structure ideas and arguments.
Quite a lot of PvP, city scale and 1v1. Loved it.