The WMPI™ package form Critical Software S.A., Portugal, is a middleware for cluster computing implementing the MPI standard (Message Passing Interface). It enables the development of portable, parallel applications to run on low-cost clusters of computers to solve performance problems in domains such as biotechnology, aeronautics, chemistry, automotives and space. Computing clusters and computing grids are required e.g. to process the huge amount of data generated by the instruments on board satellites such as ENVISAT. The strategy is to use a group of several networked computers to process data that would typically take one computer many hours, days or weeks. Additionally, using a cluster instead of a dedicated and proprietary supercomputer is more effective in terms of price/performance. Current large initiatives with clusters/grids are underway in space (promoted by ESA), biotechnology (for genome mapping) and physics (such as the CERN Large Hydron Collider).