I would have thought that the ability to create/edit plain text (*.txt) documents is extremely basic, and something that would be very useful for note taking, documenting the content of a folder and many more things. However this seems to be not supperted either in the Android or the Web app.
Something that has become a standard on many cloud-based sites is to also support Markdown documents (*.md) which are like text documents but can be viewed in a formatted nice way. This is also not supported but would be extremely useful to have in the Android and Web apps.