https://etherpad.org/ is a highly customizable online editor providing collaborative editing in really real-time .
https://mattermost.com/ is a flexible messaging platform that enables secure team collaboration
Discourse discussion platform built for the next decade of the Internet. Use it as a mailing list, discussion forum, long-form chat room, and more!
Weblate is a libre web-based translation tool with tight version control integration. It provides two user interfaces, propagation of translations across components, quality checks and automatic linking to source files.
Wekan is a kanban board which allows a card-based task and to-do management.
https://icinga.com/ monitors availability and performance, gives you simple access to relevant data and raises alerts to keep you in the loop.
https://wazuh.com/ is a security monitoring solution for threat detection, integrity monitoring, incident response and compliance.
https://nextcloud.com/ a suite of client-server software for creating and using file hosting services.
GitLab is a web-based DevOps lifecycle tool that provides a Git-repository manager providing wiki, issue-tracking and continuous integration/continuous deployment pipeline features
OpenVPN implements virtual private network (VPN) techniques to create secure point-to-point or site-to-site connections in routed or bridged configurations and remote access facilities.
SecureDrop is a whistleblower submission system that media organizations and NGOs can install to securely accept documents from anonymous sources.
http://www.postfix.org/ is Wietse Venema’s mail server that started life at IBM research as an alternative to the widely-used Sendmail program.
Hugo a static web site generator.