Codestream is a messaging platform for developers... It keeps track of conversations around a code base for future reference and learning reasons behind certain decision. Heard about it from a Goto Conference talk video on YouTube where one of the team members talked about the problem if solves. It's really impressive for projects collaboration and favorable when teams are mostly remote of come-and- developers. Especially D development. It integrates with git beautifully. I really recommend you check it out, even if you're not using git. Especially for D core development.


https://help.codestream.com/hc/en-us/articles/115003614932-What-is-CodeStream-

 I don't know much about their pricing model though...its still in private beta...you can request on their website to try it out.
It's genuine a creative solution IMHO...and difficult challenge as well.

If you're aware of Visual Studio Code's Live Share feature, then you know how powerful it can almost eliminate the gap between teams in the same room and remote teams.