There are currently two major schools of web application development frameworks: request-based and component-based.
Request-based frameworks are very close to the original CGI specification. They use controllers and actions that directly handle incoming requests. Each request is fundamentally stateless. With the introduction of server-side sessions, a certain degree of statefulness has been achieved. The different frameworks basically differentiate themselves by the way they map logic to URLs and how data is structured and provided to the developer.
Component-based frameworks abstract the developer away from the internals of the request handling and encapsulate the logic into reusable components, often independent from the web medium. The state is automatically handled by the framework, based on the data that is present in each component instance. Together with some form of event handling, this development model is very similar to the features offered by desktop GUI toolkits. The different frameworks basically differentiate themselves by the provided component API and how components are combined together.