Top Alternatives to Mattermost

Slack is a leading cloud-based platform designed for team communication and collaboration. It offers a central location for conversations, file sharing, and app integrations, enabling teams to work more efficiently and stay connected regardless of location.

Viber is a comprehensive messaging and VoIP application enabling free and secure calls and messages to users worldwide. It offers robust features for both individual and group communication across various devices.

Discord is a versatile free communication platform designed initially for gamers but now widely used for communities of all types. It offers voice and text chat, video calls, and robust server customization for groups of any size, providing a centralized hub for real-time interaction and community building.

Jitsi is a free and open-source suite of secure, flexible communication tools. It offers multi-platform support for voice (VoIP), video conferencing, and instant messaging, emphasizing privacy and ease of use with no account required to start a meeting.

Glip, by RingCentral, is a comprehensive team collaboration platform combining real-time messaging, video calls, task management, and file sharing into a single, searchable hub. Designed to streamline communication and workflow, it aims to replace disjointed tools with a unified digital workspace.

fluxday is a free and open-source task and productivity management solution designed specifically for growing startups, focusing on streamlined task workflows and team accountability.

Matrix is an open network for secure, decentralized real-time communication. It provides a flexible protocol for developers to build collaborative applications like instant messaging, VoIP, and video conferencing, enabling seamless communication across different service providers.

Let's Chat is a self-hosted, open-source messaging application built for small to medium-sized teams. It provides persistent chat rooms, private messaging, and collaboration tools, prioritizing ease of deployment and control over your data.

TribeScale is an all-in-one platform designed to streamline team coordination, encompassing communication, goal management, task delegation, and progress tracking to enhance productivity and alignment within organizations.

Grape is a powerful and flexible API framework for Ruby, simplifying the development of REST-like APIs. Designed to run on Rack, it seamlessly complements existing web frameworks like Rails or Sinatra, providing a clean domain-specific language (DSL) for building robust and well-structured APIs.

Flock is a comprehensive communication and collaboration platform designed for teams. It streamlines workflow and enhances productivity through integrated messaging, project management tools, and seamless file sharing within a secure environment.

Zulip is a powerful open-source group chat application designed for team collaboration. It uniquely structures conversations around topics, enabling users to easily catch up on important discussions and manage information overload. Zulip facilitates secure communication with integrated file sharing and various integrations.

Flowdock is a collaborative team workspace combining group chat, inbox, and integrated tool notifications. It streamlines communication and information flow for agile teams, connecting conversations with project management and code development tools like GitHub, Jira, and Trello.

Dialog Messenger is a robust, feature-rich enterprise messaging solution designed for businesses prioritizing security, privacy, and control. Available for both private server deployment and cloud hosting, it facilitates secure text, voice, and video communication across multiple devices, enabling seamless collaboration and real-time interaction within organizations.

Gitter is a free and open-source instant messaging and chat service designed specifically for developers and users of GitHub projects. It provides real-time communication within the context of software development teams and communities.

Hack Chat is a refreshingly simple and open-source chat application designed for immediate, no-nonsense communication. Forget complex sign-ups and cluttered interfaces; Hack Chat gets you talking instantly in various channels.

YakYak is an unofficial desktop client for Google Hangouts, providing a dedicated application experience outside of a web browser with features focused on convenience and improved usability.