The document discusses developing SIP applications using OpenSER, WeSIP, HTTP and Java. WeSIP adds a SIP servlet programming layer to OpenSER, allowing developers to build SIP and HTTP applications using Java. WeSIP integrates OpenSER, which provides low-level telephony functions, with the SIP servlet and J2EE environment to provide application logic and trigger services. The document provides examples of SIP application types that can be created using WeSIP and OpenSER.