- [Mattermost](http://www.mattermost.org/) - Open-source, on-prem Slack-alternative. It can be integrated with Gitlab. ([Source Code](https://github.com/mattermost/mattermost-server)) `AGPL-3.0/Apache-2.0``Go`
- [Mibew](https://mibew.org) - Mibew Messenger is an open-source live support application written in PHP and MySQL. It enables one-on-one chat assistance in real-time directly from your website. ([Demo](https://mibew.org/demo2), [Source Code](https://github.com/Mibew/mibew)) `Apache-2.0``PHP`
- [Node-Chat](https://github.com/IgorAntun/node-chat) - Not-so-basic open-source chat with admin features. `MIT``Nodejs`
- [OTS](https://ots.fyi/) - One-Time-Secret sharing platform with a symmetric 256bit AES encryption in the browser. ([Source Code](https://github.com/Luzifer/ots)) `Apache-2.0``Go`
- [Papercups](https://papercups.io/) - An open source live customer chat web app written in Elixir. ([Demo](https://app.papercups.io/demo), [Source Code](https://github.com/papercups-io/papercups)) `MIT``Elixir`