Slack, HipChat race to replace office email

Why is it that there's a surge of chat clients nowadays?

- Slack, HipChat (the latter I can't use it in my coworking space because it requires everyone to use the same email domain)

- 38 days ago Hack.chat - https://news.ycombinator.com/item?id=9863152

- 79 days ago RocketChat https://news.ycombinator.com/item?id=9624737

- Yesterday Heim/Euphoria - https://news.ycombinator.com/item?id=10068943