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).
One of the OERu's most compelling technological capabilities is the set of internally developed open source tools that allow us to automatically transform and inject a collection of MediaWiki content on WikiEducator (usually in form of micro-courses) making up a course into a mobile-friendly, easy-to-navigate WordPress site, usually situated on OERu's Course WordPress Multisite implementation.
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.
SkFor any website that requires anyone (users or even just a few admins) to transfer secrets to and from it, you want to ensure the data is end-to-end encrypted. Today various browsers (like Firefox) give warnings when you're sending secret data (like passwords) "in the clear", namely unencrypted.
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).