The revolution in web world led to increasing users’ needs, demands and expectations. By the time, those needs developed starting from ordinary static pages, moving on to fully dynamic ones and reaching the need for services and applications to be available on the web!.. Those demands changed the perspective of our web today to what’s said to be a cloud of computing that aims mainly to provide applications as services for web user. As time goes by, applications were just not enough; users needed their applications and data available anytime, anywhere. For these reasons, traditional operating system functionality was needed to be provided as a service that integrates several applications together with user’s data. In this book we present the detailed description, implementation and evaluation of SEWOS a semantically enhanced web operating system- that provides the feel, look and mimic traditional desktop applications using desktop metaphor.