The Pajé visualization tool provides interactive and scalable behavioral visualizations of the dynamics of the executions of parallel and distributed applications.
Parallelized GDB: a tool for debugging parallel programs written in MPICH.
Written in C++ and on the brink (hopefully) of usability. Please help develop!
The Minions programming language makes it easy to write performant, highly parallel programs. Minions are especially good at web apps. Minions like the web.