An activity wall which works?

I am looking for a plugin which can make an acitvity wall for people to post on, essentially like the normal comments form, except only logged in people can use it, and you only have to type what you want to say.. Essentially like making a facebook post, except it is a wall which anyone on the site can post on..
Sorry if this is a confusing description, its hard to describe, this enjin site has what i would like, on its front page:
http://hexicraft.enjin.com/

I’ve been searching around but there is nothing out there which works like that, as far as i can see..