Grape!

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.

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.

Gitter is a chat and collaboration tool for developers and users. It's a place for developers to talk.

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.

dialog app is built and designed for corporate communication on all types of mobile devices - tablet, mobile phones etc.

Campfire is a simple web-based real-time group chat tool for business. It makes real-time communication with 2-60 people as simple as visiting a web page.

Whaller lets you create private social networks and bring them to life.

qiscus is a messaging system designed to mimic working environments by allowing users to structure their teams or projects in room-based discussion system thereby removing the need for other communication tools such as emails, messaging or video chat.

TribeScale is a startup that aims to enhance teamwork in companies through the improvement of communication, coordination, and the pace on the basis of targets set. It is designed by taking as a reference the methodologies of the most innovative teams in the world: (Apple, Tesla, Google, Virgin...).Companies that use TribeScale have said that it has ended with 80 percent of working meetings. We are a platform for communication and management of teams very advanced and action-oriented, with functionalities such as creating and assigning tasks, sending surveys, decision-making, and automation of processes. »

Fleep is a messenger for your teams and projects. It enables communication within and across organizations - be it your team chats, project communication or 1:1 conversations.