A while back, I wrote about the models from kitHAUS. The product features an aluminum framing system called MHS (Modular Housing System) developed by US Systems LLC:

"Our modules are constructed on site in a matter of days, not months, and because of [the framing system's] lightweight properties can get into the hardest [to] reach places, without heavy equipment."

I had the chance to see the system for myself at the CA Boom show, and thought it was quite impressive. Clamps are used to hold the structural members together; bolts are only used to tighten the clamps. The kitHAUS reps did inform me that power tools are necessary to tighten the bolts, as hand tools wouldn't achieve the proper torque.

The system manufacturer's website has images, and even a cool video (MHS.WMV at the bottom of the main page) to show how the system comes together. For those interested, there are detailed reports on the structural testing of the system.