WebObjects is a commercial application framework produced by Apple. It is designed to make it easy to field web applications. It includes a database persistence layer that works in conjunction with an object-to-relational mapping, template-based separation of presentation from business logic, support for clustering and application lifecycle management, and a number of other features. Web-CAT is built on top of WebObjects.

You can find out more about WebObjects from Apple: http://www.apple.com/webobjects/.

The company 360 Works, which uses WebObjects in their products, also has a nice page describing the benefits of using WebObjects: http://www.360works.com/webobjects.html.