Boeing’s Bird of Prey was a low observable technology demonstrator that flew in 1996. In addition to testing features of low-observable (so-called “stealth”) technologies, the Bird of Prey also tested new materials, manufacturing, and advanced aerodynamics. Design features were also incorporated in the Boeing X-45 UCAV.
The flight test program ran for 38 flights and cost about $67 million.
Below is a video highlighting some of the aircraft and program features:
Below are some pictures (h/t The Brigrade) featuring the aircraft in flight during the flight test program and as she currently appears in the National Museum of the USAF: