Chanty!

Riot (formerly Vector) is an opensource interoperable app running on Web, iOS and Android. It is built around chat rooms, both public and private and provides messaging, filesharing, voice and video conferencing (beta on Android and web), integrations to tools like GitHub, Jira, Jenkins and much more soon. Vector is built on the Matrix.org open standard which provides bridges to other systems such as Slack, IRC and a lot more soon. One can use the hosted service or run their own. »

Mattermost is an open source, self-hosted Slack alternative.

Matrix.org is a growing ecosystem for open, decentralised chat, VoIP and IoT communication.

Rocket.Chat is a Web Chat Server, developed in JavaScript, using the Meteor fullstack framework.

HipChat is an instant messaging service designed for companies and teams. It has persistent chat rooms, one-to-one chat, searchable chat history, file sharing via drag & drop and clipboard, inline image previews, an API, chat over SMS, and more.

Self-hosted chat for small teams.

hack.chat is a minimal, distraction-free chat application.Channels are created and joined by going to https://hack.chat/?your-channel . There are no channel lists, so a secret channel name can be used for private discussions.

With Samepage, you can put all your project information on one page and collaborate with your team in real time. Samepage brings together an entire suite of project management tools, awesome communication features, and built-in integration with the apps you use. Everything you need to move projects forward, without leaving Samepage.

Yammer is revolutionizing internal corporate communications by bringing together all of a company’s employees inside a private and secure enterprise social network. Although Yammer is as easy to use as consumer products like Facebook or Twitter, it’s enterprise-grade software is built from the ground up to drive business objectives.