This paper proposes JSGrid, as a software framework to build up computer clusters running on various operating systems. JSGrid makes good use of idle computational resources without installing any software. JSGrid therefore enables various kinds of computers to be a part of a cluster, for instance, educational terminals at schools and universities, computers for development, office computers at companies and laboratories, and information retrieval terminals at libraries. An experimental result has shown that JSGrid could manage various operating systems such as Windows, Linux, and Mac OS X, and keep high throughput almost equal to theoretical prediction even under the circumstance in which dynamic join and termination of computers occurred.