Slack is a software as a service app, which is dedicated to companies in every size, from the small teams to the big organizations.
Every team which notices a lack of collaboration and communication tools should try that kind of tool in their organization.
You can use Slack to send a private message, and also communicate with the whole team.
Team members can join and leave channels as needed — unlike lengthy email chains.
Software development teams loves Slack, because of its possibility to integrate and automate with the other tools.