Contact Changed Trigger
This allows you to cause something to happen when something is changed on a contact record. It is fairly limited but still useful.
You can trigger on things like:
The Assigned User has changed, or has changed to a particular person
The DND has changed, or has changed to a particular state
A Tag has been added or removed - this is any tag rather than a particular tag.
To use the Call Status Trigger, simply go into Automation -> Workflows and click, "Create New Workflow". (1)
Then choose "Contact Changed". Afterwards, you can choose the filters or conditions under which the trigger will fire. (2, 3)