From the this is way cool department
Open-MX is a message passing stack that offers the Myrinet Express features on top of regular Ethernet hardware. It requires no kernel or driver modifications. In addition any software that support (e.g. various MPIs,PVFS2) Myricom MX libraries can link to directly to Open-MX.
The project page and software can be found here. Recently, project leader Brice Goglin gave a presentation entitled High-Performance Message Passing over Ethernet with Open-MX, why and how? You can find the slides and video at the Distributed Computing Group (DISCO) site. Quick review: I have used Open-MX since version .4 (current version is 1.04) and it is a well designed and run project that works great If you use Ethernet, check out Open-MX!