I believe very strongly in the power of documentation, for a number of reasons. Knowledge should be kept in an ordered manner, and writing documentation is a good way of not only ordering the knowledge, but double-checking it. In addition, by placing the documentation somewhere accessible, you can share it.
In December of 2016, I discovered Bear Writer. At the time, I had been using a number of different solutions for note-taking and organisation, none of which had really done the trick for me. That all changed with Bear. Arriving to critical acclaim, Bear is certainly a very pretty app, and its iCloud sync feature has served me well enough. There has just been one issue; it is only available on Apple devices.