Nearly all parallel APIs and communications APIs can be used on Linux. Anyway, the most popular are the Sockets interface, PVM and MPI. The three APIs can be used as on Beowulf clusters as on Mosix clusters.
Really, on Mosix clusters, we can use nearly all communications API, due to the ``fork and forget'' programming model. If we do a heavy use of ``/proc/mosix'' filesystem, we can take the best of our Mosix clusters. Anyway, at this time it is used a more general approachment: using standard parallel APIs to alow compatibility with Beowulfs and COWs -Clusters of Workstations-.