Dean Kamen with a 19th-century British steam engine, which he bought from the Henry Ford Museum and installed in his home.
Dean Kamen is perhaps best known for what some say is his greatest flop: the Segway. Though it didn't transform mass transportation the way Kamen had hoped, the Segway didn't stop this prolific inventor from pursuing even more ambitious inventions. Today he is working on a water-purification system for the developing world and a new kind of home furnace. The furnace he based on an early-19th-century engine. The purifier should start reaching rural villages and saving lives later this year. Kamen, whose engineering company, DEKA, is located in a refurbished 19th-century textile mill in Manchester, N.H., originally made his fortune inventing sophisticated devices for delivering medicine -- such as the portable dialysis machine. (The medical-supply giant Baxter has sold more than 500 million of this product worldwide.)