Dropbox is the best known of the end-user "cloud storage" services for documents, backups, and synchronising data among multiple devices, although now Google's Drive and Microsoft's OneDrive are functionally similar and are being heavily promoted and tied into all sorts of services.
Here at the OERu, we provide a service, attached to all of our online courses (and available to all of our partners - or anyone else for that matter) which allows anyone involved in those courses to communicate with one another from any one of a dazzling array of online "places" with WikiEducator Notes (aka WEnotes). The entire system is free and open source software (FOSS).
A few months back, I posted instructions on deploying Rocket.Chat and Wekan instances (and their mutual dependency, MongoDB) individually. Since then, I've spent some time with Docker Compose, a set of scripts which help you to define, build, and manage a set of Docker containers. Docker Compose is a thing of beauty. This is the way I now deploy Rocket.Chat, Wekan, and MongoDB together.
At the OERu we have two separate instances of market category leading Discourse Forum: one for OER partner and contributor collaborators and the other for learners. These days, online forums are seen as a bit old-school: fuddy-duddy. From my point of view, however, Discourse is "Forum-NG" (a Next Generation forum).
Wekan is an excellent, easy-to-use "kanban board" project management support tool, suitable for all manner of projects. For those who have used the highly marketed Trello kanban service, Wekan is functionally similar open source alternative that organisations can host and control for themselves. They can also enhance it in whatever ways they are moved to do so. We encourage our partner institutions to consider this path as a way of reducing costs as well as increasing freedom and privacy.