How do you document your design work?
Back in the day, companies would provide design notebooks, and even encourage engineers to have witnesses sign pages that revealed new designs (for consideration in patents). Some changes in patent law probably caused the death of that practice. I still like drawing with a #2 pencil on Ampad Quadrille paper. Like on this page
It seems archaic that people actually write stuff down, but I still do. Sad to admit this but I write on the nearest scrap of paper, like an opened envelope... if it is important I will enter it somewhere in computerland. If it sits around long enough I will forget what I was thinking and it will be thrown away. My handwriting is so poor I often cannot make out what I was thinking!
Most engineers don't use tablets, because they need to carry around a laptop to process data.
I have no real expertise in apps, but sharepoint (word, powerpoint), google docs, helpdesk... there are many ways to document designs. Collaborative tools help speed up the design process but are open to malicious intent or accidental misuse, or VPN issues. There is an entire cottage industry that will tell you what the best process is, even though the proponents have never designed anything useful in their lives.
I would be interested in hearing from other people on this topic.