Many years ago I played Cantr II. It's a text-based role playing game, but it's different to most: the aim of the game is not to "level up" or kill monsters. In fact there's no specified "goal". What you do is develop an interesting character, and an interesting storyline.
Cantr II basically forces characters to cooperate with each other: you need teamwork to do anything significant. It's also very slow paced, e.g., walking from one town to another could take around 4 real-life days.
Cantr II has multiple spawn points, with different spawn points having different languages. Many people use it for language learning (Cantr II webzine)---the slow-paced nature gives you time to write properly in a foreign language. They used to have a Chinese spawn point, but it wasn't sufficiently popular, and was subsequently removed (link).
I'd be interested to know if there's anything else available. I can't find anything else in English, but it's hard for me to search in Chinese.
Question: Are there text-based online roleplaying games which can be used for practicing Chinese writing?
What computer games provide practice? gives another example "Enter Zon", but it seems to no longer be available.
Update regarding Cantr II:
I asked a related question on LanguageLearning.SE: Is the online role-playing game Cantr II much use for language learning?. I just got an answer from the author of the Cantr Webzine:
I don't see Chinese, but if even one other person can be found (to have someone else to speak with) that may be enough to open the language again, as well as others.
(Posting this is a little bit "adverty", so I'd like to declare I'm not affiliated with Cantr II in any way.)