ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.
Epic Pen - A windows tool for drawing over your desktop and applications
Docsie - Docsie makes it easy to create and maintain your website documentation, without having to deploy it...
Gromit-MPX - Create annotations by directly drawing on your screen.
ReadMe - A collaborative developer hub for your API or code.
Ardesia - Ardesia is an usefull software for use your desktop as a Sketchpad.