What started a short list became quite a big description, more details inside the post.
Great set of CSS hover effects - iHover
PHPOffice a set o pure PHP libraries that allow to read, write and create - PHPWord, PHPExcel, PHPVisio, PHPProject, PHPPowerPoint
gitbook - command line utility for generating books and exercises using GitHub/Git and Markdown. Here is example book
uberVU / grid - drag and drop js library for two-dimensional, resizable and responsive lists
A simple overlay instructions for site interface with jQuery plugin Chardin.js