JayPad!

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.

Basecamp is a web-based project collaboration tool that allows groups of people to share files, meet deadlines, assign tasks, and centralize feedback.

Framadate is an online service for planning an appointment or making a decision quickly and easily. No registration is required.

eXo Platform is a cloud-ready enterprise portal and user experience platform-as-a-service (UXPaaS) for building and deploying transactional websites, managing web and social content and creating gadgets and dashboards. Built on open standards and open source technologies, eXo Platform has the features and extensibility of a UXP and the cloud architecture to build public and private clouds.

Zulip is a group chat app.

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.