This is 'quite off topic', but I noticedI that https://stackedit.io claims to allowing 'Simultaneous collaboration.' (you can install it locally, as well as probably a couchDb.
I never managed to make a 'plone plugin' or to 'get it to work with the (local) CouchDb, but for 'someone who knows what (s)he is doing, it is probably not too difficult.
BUT: reading the GSOC idea: GSoC 2018 Ideas: IFTTT plugin
Could it be done 'that way'. If yes, I assume there are quite a few 'similar use cases'.