Keyboard Maestro includes a variety of control flow actions which perform actions depending on a set of conditions.
The condition clause of the flow control actions can be any of:
This is followed by a set of specific conditions. If there are no conditions in the set at all, the action will not execute anything except the Until action which will execute the actions once. Neither side of the If Then Else will execute.
The available conditions are listed on the wiki Conditions page.