The Falcon040 was another prototype machine that was never released. According to Hans-Martin Krober, who has one of the prototype boxes,
the Falcon040 was in a SUN style pizza box and was larger than the MicroBox. The Falcon040, aside from sporting the Motorola 68040 processor,
would have had an optional ethernet interface as well.
Thanks to Hans-Martin Krober for additional information. Please visit Hans-Martin's The Atari Exhibition for more insights into Atari.