Rundeck is often described as Jenkins for Operations. It is a tool that can help systems administrators to create collections of tasks which complete some action on remote servers.
A task is often a command to execute on a remote server, with jobs defining a collection of tasks, and a particular execution of that job being associated with one or more nodes (servers).
Rundeck can be used as a mechanism to run common commands at defined intervals - effectivly providing a replacement to cronjobs, but adding additional reporting and visibility. Jobs can also be defined to run on at least one, or multiple nodes in a group, where Rundeck acts as an orchestrator to ensure commands are executed cleanly.
Some systems require adhoc, infrequent commands to be executed, perhaps to remove files from a memory cache, or remove stale artifacts from a directory.
Historically it may be necessary to allow a few users to have access to live servers to run these commands, however, using rundeck allows a job to be defined by a privileged user, but only executable by less-privileged users.