We use confluence, being our main documentation platform. We simply copied the template and manually create and update stuff

Confluence is a fine alternative! (we actually considered it but I think ADRs should be closer to the code, so I'll go with Markdown in the github repo for now)

I used Dropbox papers sometime when we worked a lot with ASR's. I'll actually would prefer to have then with the code, easier to keep them up to date or directly link to parts of the code.