Such 'internally driven' operations, there are many. However, actually there are much more of 'externally driven' operations, which is, 'operations which is triggered by requests from outside of the organization'. Moreover, 'externally driven' operations should be processed accurately along the rule.
Here, we would like to introduce a Workflow, which [1. Accept Entry for Joining Event] at "Form" of Google Drive (ex.Google Documents), [2. Automatic submit Thanks E-mail], [3. Payment Confirmation by human], [4. Automatic submit Thanks E-mail for the Payment]. (operation Corresponding to Acceptance of Applications for Event)
[Applications Acceptance flow]