Jylab is a portable and flexible scientific computing system favoring extensibility. It provides users with a scripting language and a core set of libraries implementing numerical linear algebra routines, communication models, interactive visualization and computer algebra system capabilities. It thus enables the development of scientific applications involving numerics, graphics and symbolics over distributed computing platforms. It is enhanced with a collection of extension packages that support Grid computing and implement Web search engine and Web graph analysis frameworks. Building a multithreaded Internet algorithmics application in Jylab is fully presented.