A large range of software environments addresses numerical simulation, interactive visualisation and computational steering. Most such environments are designed to cover a limited application domain, such as finite element or finite difference packages, symbolic or linear algebra computations or image processing. Their software structure rarely provides a simple and extensible mathematical model for the underlying mathematics. Thus, assembling numerical simulations from computational and visualisation blocks, as well as building such blocks is a difficult task for the researcher in numerical simulation. This paper presents the NUMLAB environment, a single numerical laboratory for computational and visualisation applications. Its software architecture one-to-one models fundamental numerical mathematical concepts and presents a generic framework for a large class of computational applications. Partial and ordinary differential equations, transient boundary value problems, linear and non-linear systems, matrix computations, image and signal processing, and other applications all use the same software architecture and are built in a simple and interactive visual manner. NUMLAB’s one-to-one modelled mathematical concepts are illustrated with various applications.