Slack is a popular collaboration tool that is becoming a natural choice for small- to medium-sized teams. It has a clean, intuitive interface that neatly organizes your conversations in the forms of chat rooms and associated options. Plus, it offers a free and two reasonable paid plans, which makes it a no-brainer for most teams.
Primarily replacing the use of emails to escape lengthy Email conversations, Slack helps teams discuss (and in some cases, create) tasks and projects, make voice and video calls, create groups, and add attendees as required.