Question:
Dean Kamen Water Purification?

Answer: My guess would be a practical Sterling engine (or similar heated-air engine) that can be used for a home-based electric power generator. My guess is based on the following:

1. It has been known that Dean Kamen has had engineers working on designing and building a practical Sterling engine. 2. It is apparently not a medical invention, which is one of Dean Kamen's other favorite projects. 3. The article mentioned that in a meeting with Jeff Bezos, Bezos found something amusing in the operation of the device. My guess is that Bezos made a dirty joke about the oscillatory movements of the prototype reciprocating heat engine. 4. An efficient home-based electric power generator could produce electric power using natural gas (or other fuels) at a cost that is competitive with obtaining the power through wires. The waste heat could also help heat a home in cold weather. 5. The article mentioned how cities would be changed by the invention, and that it might "run afoul of existing regulations". My guess is that this refers to the modifications of the power grid infrastructure and the and issues about whether or not power companies will have to pay people for the power their home-generators produce. 6. The article mentions that the device can be "retro-fitted". I think that the term "retro-fitted" fits better with a power source than for a transportation device. 7. The price of $2000 and up for a small power generator is about right. 8. The article did mention that it could be a new energy source, and no one refuted the claim (like when they stated it was not a medical invention). 9. It was stated that the invention would affect some "old-line companies". The power companies have been around plenty of time to be classified as "old-line", and "old-line" could be a subtle reference to old power lines. 10. Dean Kamen has been interested in inventions that would help third-world countries (e.g., a cheap water purification system). A small electric power generator that can run on many different types of fuel would be very useful in improving the standard of living in these countries.