A0

A0, A-0, A₀, or a₀ may refer to:

101 A0 and 103 A0, two versions of the German Heinkel Tourist moped
A0 paper size, an international ISO 216 standard paper size (841 × 1189 mm), which results in an area of approximately 1 m²
A0 highway (Zimbabwe), a highway which orbits Zimbabwe
A0, the lowest A (musical note) note on a standard piano
A0, a climbing grade
A00, Irregular chess openings code in the Encyclopaedia of Chess Openings
A-0 Geyser, a geyser in Yellowstone National Park
A-0 System, the first compiler ever developed for an electronic computer
L'Avion, IATA airline designator for the French airline
Characters of type A₀, an older term for algebraic Hecke characters
a₀, the accepted mathematical symbol for the Bohr radius
Haplogroup A00 and A0; see Haplogroup A (Y-DNA)

Airplanes and rockets

A-0, a 1943 Pre-production model of the German Walter HWK 109-509 liquid-fuel bipropellant rocket engine
A-0, a 1938 variant of the German Siebel Si 204 transport and trainer aircraft
He 177 A-0, a pre-production series of the 1942 German Heinkel He 177 heavy bomber
Hs 126A-0, a variant of the 1937 German Henschel Hs 126 reconnaissance aircraft
Ju 87 A-0, a variant of the 1936 German Junkers Ju 87 dive bomber aircraft
Me 210A-0, a pre-production variant of the 1943 German Messerschmitt Me 210 heavy fighter aircraft