Mattermost

An open-source, self-hostable messaging platform designed for secure team collaboration, offering features like file sharing, search, and third-party application integrations.

It supports one-on-one chats, group discussions, and team-wide conversations, organized into channels for streamlined collaboration. Originating as an internal tool for SpinPunch, a game development studio, Mattermost was open-sourced in 2015 and has since evolved into a robust platform with both free and enterprise editions. It is available as a web application and offers desktop clients for Windows, macOS, and Linux, as well as mobile apps for iOS and Android, ensuring accessibility across various devices. Mattermost emphasizes data security and privacy, allowing organizations to host the platform on their own servers or opt for cloud deployment, making it a suitable alternative to proprietary messaging services like Slack and Microsoft Teams.