We've used Confluence for some time. With one of our clients we've used it extensively. And it help to solve a lot of problems, due to bad PM skills of the other side.
Then – we stopped paying that much attention to Confluence and everything became lost in sub-sub pages. Search didn't help at all.
After some time we understood that gitlab issues were better place to document everything in non-code environment.
After some time we understood that information is either important only NOW and we use gitlab issues, or it is related to code and engineers put it into .md files in app repo.
And there is another type of documentation, that lives in DropBox folders in .docx format, that is provided to client: usage guides and all that stuff.
Wiki in gitlab also doesn't work for us. It has same problems as everything else including Confluence.
Thinking of having repo for that and sphinx doc generator.
For some reason any kind of wikis don't stick.
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We strive for transparency and don't collect excess data.