Wracking my brain, I’m sure I can recall reading (way) bitd that Keith Bontrager was working on an Aermet frame. Never seen it.
What about that prototype Yeti ARC LT with carbon (or carbon wrapped) tubes a la C-26? Can vaguely recall a trade show pic (for some reason I think it had Penske forks)
The American Beryllium?
A full sus Merlin with multiple girvin elastomers suspending multiple frame tubes (like an elevator on steriod). Vaguely recall magazine pics way back in history.. Apols for my ropey description - it makes (some) sense in my head!