Hot Corners

Hot Corners is a feature in the Desktop & Screen Saver pane of System Preferences that can be adjusted to trigger something when the mouse is moved to a corner.

Usage
The following actions or features can be triggered by a hot corner:
 * Mission Control
 * Application Windows
 * Desktop
 * Notification Center
 * Launchpad
 * Quick Note
 * Start Screen Saver
 * Disable Screen Saver
 * Put Display to Sleep