The User rights extensions category contains articles on extensions that enhance or alter the rights management system, e.g. changes to the way rights are assigned, apis, maintenance tools. It does not include extensions that merely name the rights needed to use the features of that extension. For this purpose, please fill in the rights parameter of the extension template and they'll be categorized in Category:Extensions which add rights.
For extensions grouped by the kind of actions permitted, see Category:Extensions by page action.