As a biproduct of the startup I'm working on I wrote a recurrence relation server. It takes in a JSON object representing a recurrence relation[1] and a JSON object representing an HTTP request to make. It then makes the request at each instance of the relation. Recurrence rules allow for very complicated time periods (e.g. The second last day of even months, but not any Tuesdays) and frequencies between seconds and months. It can also be used more simply just to create timed HTTP callbacks.<p>I'm looking into things which could provide a small revenue stream while the main product is ramping up, and I'm wondering if this is something useful enough that you would pay for it.<p>[1] http://www.kanzaki.com/docs/ical/rrule.html