Boot

Intel have implemented a very interesting library of C++ classes and templates, called the Intel Threading Building Block. The source has fairly recently been released under the GPL v2. Using these templates and libraries, you can easily make existing C++ code take advantage of parallelism. It's similar to OpenMP, yet different in that it's C++ and templates based.

I've still to look into this technology, but I hope to spend some more time with this now that it is Open Source.