Ravel is somewhat specialized to message-passing programs, and is used for showing the patterns of message flow as well as the lengths of message queues, in addition to the states of processes.
In Figure 3 we see ravel displaying the very same logfile as displayed by upshot in Figure 2. The display shows sixteen processes working on a solution of a Dirichlet problem in which each process carries out an update of its region of the grid, exchanges boundary information with its neighbors, and then carries out the next iteration. At the moment, process 6 is sending boundary information to process 5, processes 1, 7, and 18 can be seen by their color to be computing, and most of the other processes are waiting to receive messages. The small numbers beneath the processes give the length of the message queues. In some problems these message queue lengths provide valuable clues about bottlenecks in the computation.
It is possible with ravel to move the processes around with the mouse to achieve a pattern of processes that is particularly useful for understanding the message flow. Here the processes have been arranged into a grid that reflects the portions of the grid they are responsible for.