GridGain is an open source product written in Java providing a grid computing platform. It is known to be one of the more widely used grid product, certainly, as far as I see, one of the easiest to "gridify" or grid-enable an existing product.
One of the applications of the product is to couple with Amazon EC2 to make a "cloud" computing platform. See Gridgain + Amazon EC2
The widespread use of "multi-core" PCs also means that the product can be used to "parallelise" to take advantage of this increased power.
