WebObjects applications accept HTTP requests either directly (usually on a specific port) or via an adaptor that sits between them and the web server. Adaptors are either CGI programs or web server plug-ins (NSAPI or ISAPI).
The server processes special tags in HTML pages to produce dynamic but standard HTML. Tools are provided to easily set and get object properties and invoke methods from these tags. Applications can maintain state over multiple HTTP request-response transactions (which are intrinsically stateless). Applications can also use Apple's Enterprise Object Framework object relational mapping libraries for object persistence and database access.
Apple acquired WebObjects from NeXT, along with Steve Jobs.