"TimeTrade? is a rules-based resource management system that supports real-time scheduling of activities, services and events." For instance "[a] leading enterprise software vendor uses TimeTrade to schedule sales engineers for customer visits, product demos, conference calls, and other interactions based on the SE's skill set, certification, seniority, cost, territory and other factors."

What's interesting this software's ability to extend scheduling to the web to let customers take appointments online. Here's additional discussion on the topic (a psychologist says his internet-savvy customers love the service).