Jylab is a portable and flexible scientific computing system favoring extensibility. It provides a user with a scripting language and a core set of libraries implementing numerical linear algebra (NLA) routines, communication models, interactive visualization and computer algebra system (CAS) capabilities. It thus enables the development of scientific applications involving numerics, graphics and symbolics over distributed computing platforms. A collection of extension packages can optionally support Grid computing and implement Web search engine and Web graph analysis frameworks.