Development and system configuration notes. Maybe other notes too. We'll see.
I take a lot of notes using both paper and various applications. Software development procedures and options, system and application configuration options, lists of useful tools, services, and commands—stuff like that.
Many of my notes would be more useful to me and may also be useful to others if they were readily accessible (e.g., when setting up a new employer or client system), so I want to start posting some of my notes publicly via GitHub.
I also have several potentially useful things posted on GitHub Gist.