A softer sonic boom...

[Wing Nut]

This is pretty interesting!

http://story.news.yahoo.com/news?tmpl=s ... onic_booms

[Ivan]

Northrop Grumman Corp...
Started that resarch in the late 80's in a joint project with Sukhoi. Current state is somewhat mysterious as Grumman left the project but there could be a Sukhoi-built prototype in the testing phase

Sukhoi S-21

Still with the Grumman logo's and 2 engines, current Sukhoi prototype has one extra engine on the base of the tail
Bizjet, seats 8-10 passengers. max range 9000km @ M1.8-2.2

Plans exist for a S-51 (same general shape, 4 engines) with a range of some 10,000km at M2.0 and seats for 50 passengers

[Polynomial]

it is very odd looking rather. . .