A succinct description of Seaside features and benefits from squeak.org.

The most unique feature of seaside is its approach to session management: Seaside models an entire user session as a continuous piece of code, with natural, linear control flow. Pages can call and return to each other like subroutines. Complex sequences of forms can be managed from a single method. Objects are passed by reference rather than marshalled into URLs or hidden fields. Seaside fully supports the backtracking and parallelism inherent to the web browser.

So unlike in the Java servlet model seaside does not need a separate handler for each page or request.

Other features

• a callback-based event model
• a "transaction" system for auto-expiring pages
• programmer-friendly HTML generation
• a system of reusable and embeddable UI components
• web-based development tools. If an error occurs you may fix it by using the web browser and resume the execution.