Nextcloud is an open source, self-hosted file share and communication platform. Access and sync your files, contacts, calendars and communicate and collaborate across your devices.

Mattermost provides high trust collaboration and messaging solutions through an open source, community-powered approach. Enjoy all the productivity benefits of workplace messaging across web, mobile and PC, with unlimited archiving, search and integrations within IT-controlled private environments in public clouds, including AWS and Azure, as well as on-premise in private clouds and virtual or physical servers.

Kimai is a free open source timetracker. It tracks work time and prints out a summary of your activities on demand. Yearly, monthly, daily, by customer, by project, by action …