Most crossbow manufacturers include a sight system with every crossbow they produce. Three types of sight systems are the red dot, scope, and peep/pin.
Red Dot Sight: Most crossbow manufacturers offer mounts for scope or red dot style sights.
Scope Sight: Most crossbow manufacturers offer scopes that are specifically designed to match the ballistic performance and vibration of a crossbow.
Peep/Pin Sight: This sight system includes a rear sight "peep" with a blade and pin front sight.