[donaldguy]

It has @mentions, notifications, and the ability to have some Google-Docs style inline comment threads, so depending on the use case I'm not sure you'd totally miss it

Otherwise perhaps phacility-hosted (so cloud) Phabricator, wherein it is mostly (a less unified UI) project management system but has the realtime chat component available in https://www.phacility.com/phabricator/conpherence/