Actions are 'programmed' admin tasks which can be performed by selected regular users from the Task Center. An action could be creation of backend users, fixed SQL SELECT queries, listing of records, direct edit access to selected records etc.
This extension allows to run some TYPO3 backend administration tasks like the creation of new backend users as a non-admin user if properly set up. It hooks into the taskcenter extension for the GUI part.
The functionality was part of the TYPO3 Core until TYPO3 v10.0, and moved into its own extension, receiving its own public repository.