Is one really needed? Facebook has VOIP, Slack has VOIP, most modern games have decent built in VOIP. It's not an interesting problem anymore and it's available everywhere.
Network effects. Skype is the only thing resembling a de facto standard for talking to any two random non-technical people. Skype has literally 100x the monthly active users of Slack, and barely anyone is on slack to make VOIP calls, especially with people outside of their team.
That's what WebRTC promises to solve, and there are already great tools using it (Appear.in for example).
What they don't solve is the discovery/network aspect.
My own side project/startup wannabee uses WebRTC to enable random non-technical people to talk to companies that use our product :) ( https://keveo.tv/en/ ).
Then it's good enough. Facebook is bigger than Skype and you can have a chat/VOIP call with anyone on Facebook, even if they're not your friend. Then there's Google hangouts as well. Slack is meant for teams. Gamers use Discord.
