I'll admit, comboEditable is an extremely dry name for an open source project (I would have used something like Project Bierstadt but it's not really that descriptive). Like everything else I develop and share publicly, this came out of necessity.
In Windows there is a UI concept of an editable combo box. Basically you're given a drop down list of options and if you can't find the option you're looking for, you just type in another (see the demo if you're having trouble visualizing). This concept does not exist on the web or anywhere outside Windows applications. I assume that UX designers across the globe unanimously decided that an editable combo box is a UI kludge, but I still think it's a handy control.
It is an unintrusive jQuery plugin that uses the regular HTML DOM as input and transforms into an editable combo box (a text box, hidden field and several divs, if you're wondering). The unintrusive part means that if scripts are disabled, the user still gets a combo box, just not an editable combo box.
If you find yourself in need of an editable combo box, head over to the jQuery plugin page or download it at github. Also, take a look at the demo to see usage.