Vérinage

Apparently the French have been demolishing buildings 9/11-style (sans aircraft) for quite a long time and consider it a standard demo technique, called "vérinage". The general idea is that the weight of the top portion of the building, even though it can be supported by the building, contains such a massive amount of potential energy that once it's fallen a story or two it can easily sheer through any and all support beneath it.

To my uneducated eye this looks exactly like the World Trade Center's collapse, especially in the three aspects of

1. Massive ejection of dust & debris
   
2. Near free-fall appearance ("near" because if you can eyeball the difference between a 9.8 m/s*s fall and an 9.0 m/s*s fall, you're a better man than I)
3. Sheer vertical collapse similar to standard U.S. explosives-based demolition.

While I cannot declare with absolute certainty that the twin towers falling was the work of physics and not a nefarious plot by an evil vice-president and his secret legion of freedom-hating evil-doers, it's good enough for me.     :D

"A compilation of demolitions conducted using the French demolition technique of vérinage. This is achieved with hydraulics that push structural members out of alignment, allowing the top portion of a building to then demolish the structure below via gravity alone, without the use of explosives. Note that the collapses are rapid and produce copious dust."