The first aircraft that was created was the
RE 2000, single wing airrcraft, with metallic frame and powered by a
radial 14 cylinders engine.
From that aircraft two aircrafts
were developed almost at the same time: the RE 2002, equipped by a more
powerful radial engine, and the RE 2001 with a V12 engine.
The Re2003 was the two-seats version of the RE 2002 (the first prototype was a modified RE 2000 though).
The Re2005 was designed from the RE 2001 but replacing the power unit by the more powerful DB605 V12 engine.
Only one unit of the RE 2006 was built, designed to host a DB603 engine. It didn't have the chance to fly.
RE 2007, the fighter with jet engine, is still an open point nowadays.
Mr. Longhi always claimed that the design was ongoing during WWII. Some
documents are post-war. Only one document, at the moment seems to be
from the WWII period.