Top Alternatives to Gitter

Slack is a cloud-based team collaboration tool.

Discord is a freeware proprietary VoIP application designed for gaming communities.

Glip is fully searchable, real-time group chat; video chat, task management, file sharing app.

Mattermost is an open source, private cloud Slack-alternative, Workplace messaging for web, PCs and phones. MIT-licensed.

Matrix is an open protocol for real-time communication. It is designed to allow users with accounts at one communications service provider to communicate with users of a different service provider via online chat, Voice over IP, and Videotelephony.

TribeScale is an All-in-One platform to coordinate your team around what really matters - communication, goals, decisions, tasks and results.

Grape is an REST-like API framework for Ruby. It's designed to run on Rack or complement existing web application frameworks such as Rails and Sinatra by providing a simple DSL to easily develop RESTful APIs.

Zulip is a chat and collaborative software.

Flowdock is a group chat for teams which integrates with GitHub, Jira, Trello.

Dialog Messenger is a handy and feature-rich enterprise multi-device messenger available for server or cloud.

Hack Chat is a minimal, distraction-free chat application.