I have previously provided an in-depth explanation about NextCloud with Collabora Office Online and how we've installed it on Ubuntu 16.04. This is an update both of the process, and of the technology.
Update 2021-11-08: this post is now getting a bit long-in-the-tooth, and I need to update it to use up-to-date components. It might still be useful to folks, but use it with caution. Also, please note, we're using NextCloud with OnlyOffice (the open source community edition) these days.
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).