Teamder - Tinder, but for creating teams at work.
Slack - A messaging app for teams who see through the Earth!
PullReminders - Review and release pull requests faster with Slack reminders and metrics.
9mCollab - Collaborate (efficiently) Conclude (fast) Contribute (in the knowledge base)
Monolist.co - The command center for engineers. Tasks, pull requests, messages, docs — all in one place
Mattermost - Mattermost is an open source alternative to Slack.