The core difference is that TalkJS includes a full fledged messaging UI and well-designed email/sms/push fallback*. In working on earlier startups, we noticed that reliable realtime data transfer was the least of our problems. Having a good cross-browser messaging UI, for mobile and for desktop, that loads fast, works everywhere (including, say, IE9) and makes people happy was a lot more work.

TalkJS came to be when we realized that many companies spend a lot of effort in reinventing this wheel over and over again, and that all of them ended up building very similar UIs.

Think of TalkJS more like a user-to-user Intercom than a Sendbird.