I built something similar a few years ago. Basically yammer but hash tags and @ references interact with plugins. So #bug would make a bug, and "@This Person #remind me to contact them" would create a reminder in the reminder plugin for me to contact this person (with their name linked to contact data in the contact plugin).

I've had several people tell me they wish it was still up and I won money for it in a university contest. I'm not really sure what to do with it now.