Dealing with recurring dates isn't easy, but one way of adding a layer of structure to projects that must deal with them intelligently is by following standards like iCalendar. Johannes Raggam sent in jquery.recurrenceinput.js (GitHub: collective / jquery.recurrenceinput.js, License: MIT), which is a UI widget that is compatible with RFC5545.
The widget allows various repeat rules to be selected and then outputs a string that should be usable in ICS files.
HeapBox (GitHub: FilipBartos / heapbox, License: MIT) by Filip Bartoš is a
select replacement. It has an event-based API, supports standard features like disabling the control, and has some nice flat UI themes.