You're describing Google Wave¹, which (sadly) was killed as unsuccessful.
Still wondering whether it was unsuccessful as a product or as a concept.
Can we even distinguish those in practice? AFAICT its main problem was being so general-purpose that it was hard to describe as a compelling use case.
Of course, I also don't subscribe to the belief that the popularity or memetic prowess of an idea defines its "success" except commercially. I thought it was a very nifty thing. To me, that counts as a success. Alas, that is not the metric used by companies. :p
Sounds a lot like Google Docs.
Maybe all this time that Google has been struggling to develop the killer chat app, they were sitting one the ultimate one this whole time.