Last updated: 2020-10-26
Works with CiviCRM 4.7. It might not be supported anymore.
CiviRules is an extension that allows rules based actions, like automatically adding a contact to a group when he/she contributes more than xxxx.
A cookbook on what this extension could be used for: https://docs.civicrm.org/civirules/en/latest/
More technical details and tutorials how to create your own stuff: https://docs.civicrm.org/civirules/en/latest/create-your-own-introduction/