Charm++ is a portable adaptive runtime system for parallel applications. Application developers create an object-based decomposition of the problem of interest, and the runtime system manages issues of communication, mapping, load balancing, fault tolerance, and more. Sequential code implementing the methods of these parallel objects is written in C++. Calls to libraries in C++, C, and Fortran are common and straightforward. Charm++ is portable across individual workstations, clusters, accelerators (Cell SPEs and GPUs), and supercomputers such as those sold by IBM (Blue Gene, POWER) and Cray (XT3/4/5/6). Applications based on Charm++ are used on at least 5 of the 20 most powerful computers in the world.
RunJRun is a very simple system for doing parallel processing in Java, using Amazon Elastic Compute Cloud (EC2) instances as compute nodes. The basic compute unit is a Runnable, Serializable Java object, a "task" for short. A user submits a list of such tasks to RunJRun. Each task then has its run() method invoked on an EC2 instance. To use it, you'll need an Amazon Machine Image (AMI) that has the RunJRun server-side software installed; several such AMIs are available.