As a different, more techy, solution that can work depending on the people you collaborate with, is to use a hosted Git service for collaboration (if you want to stay completely open source, a self-hosted GitLab).

Then, change your publication workflow to write in Markdown, ReST, or one of the other ascii formats that previews correctly, and set up your CI to render the documents automatically into, e.g., pdf:s using a converter (which can be done as part of the CI). There are all kinds of converters from Markdown/REsT -> docs, presentation, etc. formats that are as competent - if not more so - than the usual office suites. This setup offers both online editing in the GitLab instance and offline by local cloning of the Git repo.

The side effect is that this system very seriously records and preserve your document history. You can see exactly who, at what point, changed, added, and removed things. For some types of documents, this can be very important.