SwissBike,a Division of Montague Corporation offers a very cool folding Mountain bike. The folding design is derived from a Military project funded by DARPA.

In 1997 Montague partnered with the US Marines to develop the Tactical Electric No Signature (TENS) Mountain Bike. Montague developed a new folding frame design called the X-Series, integrating the F.I.T. (Folding Integrated Technology) system into the frame design. The non-electric version of the TENS Mountain Bike, named The Paratrooper, became available shortly thereafter.
Now the consumer version of the folding mountain bike is sold under the SwissBike brand.

There are three models of the SwissBike available. The SwissBike XO is the flagship model, sporting the Sram XO drive train and Montague's patent pending CLIX wheel release system. This model is made in Switzerland. The XO has an MSRP of $1,995.
For those who like the folding feature but are on a budget, the LX (MSRP $795) and the TX (MSRP $645) offer the same Swiss knife-like folding with Shimano's 24-speed and 21-speed drive trains and Montague’s patent pending CLIX wheel release system.
The SwissBikes sell online at the SwissBike site. See also Montague's Military Bike site.