SharePoint is essentially an HTML + JScript + MSIE-DOM interface to a network file share full of MSOffice documents. It's a modular ASP.NET application with some modules that help you use the Web to emulate the shared folder setup your IT middle-managers know and love. There are some minor modules, such as a lame survey system. There are hooks for integrating with InfoPath for simple form <-> database apps, and WWF for "workflow" (state machine), and SAP for ... ERP goodness I guess.