Rundeck is yet another one of those services that I want to get my hands on but haven’t yet got the time to. The simplest way to describe it is: cron on steroids.
Rundeck allows one to define the commands and then allow for execution on those commands manually, periodically or based on a certain trigger. Imagine, for example, a deployment command that needs to run across some servers to which you are not comfortable giving access to developers, or even non-technical users. You can create a command in Rundeck and give access to certain users to execute it, via clicking a button or two in a user friendly web interface.
A side benefit to using Rundeck versus cron are the metrics. Rundeck collects metrics like successful and failed executions, execution times, etc. So it makes it easier for you to see that certain jobs are getting progressively slower or fail on specific weekdays, etc.
The best part is that Rundeck is Open Source and self-hosted, so you don’t need to give sensitive access to some external web service.