The plone.formwidget.recurrence package provides a z3cform widget for recurrence.
The main GUI work is done with the pat-recurrence pattern from mockup.
This widget provides a simple textarea where a RFC 5545 compliant recurrence rule can be entered, if javascript is not available.
The resulting value of the widget is a RFC5445 compliant recurrence rule string, ready to be used with python-dateutil's rrulestr.
You need to add plone.formwidget.recurrence to either your buildout, or your product requirements. For example:
[buildout] eggs += plone.formwidget.recurrence[z3cform]
or:
install_requires=[ 'plone.formwidget.recurrence[z3cform]', ]