It moved from Objective-C to Java under Apple. Apple discontinued shipping it with OS X Server Snow Leopard, but the frameworks are still available/free. The community picked up where Apple left off with the open source Project WOnder.
It is a full stack development framework. Enterprise Objects Framework(EOF) is the ORM or Model layer like Cayenne or Hibernate. WebObject components are the front end View layer like you might get from Tapestry.
I have yet to find a web framework that rivals its Controller layer, DirectToWeb (D2W). D2W sits between the Model and the View. It can generate Views automatically using information from the model and with customizable direction from a rule system. It also provides controller actions with customizable callbacks.
Out of the box, WebObjects can reverse engineer your database, constructing a full model of it, and D2W can then construct a full blown Create/Read/Update/Delete interface to it with no coding required. If you don't have a database, you build a model and WebObjects can generate the SQL necessary to create the database for you as well.
It's still pretty amazing, despite being treated like an ugly step child by Apple. It still powers the billion dollar iTunes store as well AFAIK.