A very specific fork of "DatePicker, Yet another jQuery-based date picker," built for Khan Academy.
Specifically, this is meant to enable date range selection functionality very similar to Google Analytics'.
See these screenshots of DatePickerKA in action and then learn more from https://github.com/foxrunsoftware/DatePicker and http://foxrunsoftware.github.io/DatePicker, which is where the real documentation and API lives.
License: MIT.