This is a simple plugin to expose some private WordPress query vars.
For example, you can set “category__not_in” by GET, POST or cookie and it will be automatically passed into WordPress. This is not very useful on its own, but can be a powerful base for allowing users to customise their experience of your site. For example, with a simple front end (which I might build one day!), a user could choose to ignore some categories of a blog. This was mostly inspired by my mother and aunt complaining about some of the technical posts on my blog.
The code is all hosted on wordpress.org. If you have a question, you could post it below. This is really a plugin for developers so I recommend you read the code before asking here.