Ask HN: Best centralized chat?

I want to centralize chat and notifications for my small company. We're only 3 people right now but here's a few channels we might need:

- deploy: every time something goes live with details

- chat: simple text chat

- calendar: events from the company calendar (sent via a cron/cli on my linux server)

Must work on the web and have native Android and Windows phone apps (synchronized messages, notifications). Also, how exactly does it work when you have the same account open both on the browser and mobile? Will it keep pushing notifications twice?

Right now Slack seems way more popular but I hear at least once a week somebody complaining about it on Twitter. I know about mattermost but I already self host too much stuff and it adds overhead.

Right now I'm inclined to choose Slack or Telegram.