Mattermost alternatives

Open source, on-premises, Slack-alternative. Like Slack, you can send messages and files across channels, get notifications on unreads and mentions, and search history–all from your PC or smartphone.
Mattermost alternatives are:
Here are the latest news about Mattermost:

2015 Mattermost - open-source, on-premise Slack-alternative

GitLab, the git repository management provider, and YC alums SpinPunch have launched Mattermost, an open source, on-premises messaging app (like Slack). Many larger organisations run all software on-premises, often because of security, scale and control, but Slack doesn’t offer an on-premises version. Developed as a team communication service Mattermost allows users to send messages and files across various channels, receive notifications and/or alerts and search history on PC and smartphone. You can implement hashtags to organize messages and threads, create team-specific color theme and archive important communication for future reference. In short, a much easier and more efficient way for remote teams to work together and exchange messages when compared to email (starting to sound like a dinosaur at this point).