except for the fact it isn't quite dead:

http://blog.caranddriver.com/new-spin-mazda-files-patent-for-new-gen-rotary-engine-heres-what-it-tells-us/

I can't argue with a single thing he said, but for a power to weight ratio, the rotary can't be beat by pistons.
For an insane story about how it was conceived, you can't beat the Wankel period.

A few months ago, a series of misshaps, including accidentally drilling into a live wire (who put that there?!), led to the death of my rotary hammer's suppression capacitor (see 7:03) -- the holy-fuck-what-just-blew-up kind of death that shorts out the entire circuit, dragging the fuse along into its early grave.

It was an absolute pain in the ass to find a replacement capacitor for a 21 year old Bosch GBH 2-24 DSE, but given how robust that machine has been over the last decades, it was worth it.

Good catch. I just cut and pasted YT description, but will fix.

D'oh. You got me. That cordless phone would have been rotary back then. Changing it back....you bastard.

Your video, Brilliantly Simple Rotary Wood Splitter, has made it into the Top 15 New Videos listing. Congratulations on your achievement. For your contribution you have been awarded 1 Power Point.

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We had a rotary phone and our number ended with 9900, people hated calling us. I remember when you made a long distance call on it and the operator would come on my mom would tell her our number to bill it to. They were so trusting back then.

*related=http://videosift.com/video/Rotary-Engine-CGI-Demonstration

Very good explanation of how Wankel/Rotary engine works has been added as a related post - related requested by kulpims on that post.

Rotary Engine CGI Demonstration has been added as a related post - related requested by kulpims.

Eh, it has wings, they are just on top.

Hence rotary wing aircraft.

A rotary (Wankel) engine has a triangular device that acts as the piston, which rotates in a chamber close to a figure 8 shape. Each side of the triangle acts as it's own piston as it rotates, first intake through a port (no valve) then compression, detonation, expansion, and finally exhaust through another port (still no valve).
Radial engines (what I think you meant) are relatively normal piston driven engines where the pistons are arranged in a circle around the crank at a 90 deg angle from the cranks rotation. These are usually used in prop driven airplanes.
This motor arranges the pistons in the same orientation as the cranks rotation...a 90 deg difference from radial engines. This makes it far more compact, but also puts the pistons in a single, rotating, revolver like arrangement of cylinders. It's a bit of a combination of rotary and radial engine features.

How is this different, or more efficient, than a Rotary Engine:
http://en.wikipedia.org/wiki/Rotary_engine

(Videosift should add support for HTML links... wait, what?) @dagg

Revolutionize, probably not. Be an improved option over 'regular' internal combustion in (apparently) weight, size and efficiency, maybe. This seems to be a great option for a hybrid. Being smaller and lighter is what you want in an energy efficient vehicle, as is fuel efficiency. Since fossil fueled vehicles will be the norm for the foreseeable future, any step towards making them more efficient is a good thing (although not the end goal, true enough). This seemed to have many advantages of Wankel motors (rotaries) without the efficiency problem due to low compression/incomplete combustion. 14:1 on pump gas is INSANE! My offroad race motor is only 12:1 and it needs trick racing fuel.
Also, as far as simplicity, this had no valves and assorted crap, just inlet and outlet ports (from what I understood anyway) like Wankels. That's a HUGE jump in simplicity, with an entire system eliminated, so there's far less to break/wear out/need tuning. IF manufacturing cost can be reasonable, I see this as a great step forward possibly making hybrids more acceptable to many more people.

These little rotary- *winged craft are pretty fun to fly!