The XM803 was a joint US-West German project to replace the M60. Unfortunately, cost overruns and disagreements (The US wanted the Shilelleigh 152mm gun/launcher, the Germans wanted a 120mm smoothbore gun) led to its cancellation. The US came up with the Abrams, and the Germans the Leopard II.
The Soviet T-35 was perhaps the ultimate in "Land Dreadnaughts" with four turrets, one with a 76.2mm gun, two with 45mm guns (one fires rear), and one with a machine gun. 60 were built.
Being humongous targets with surprisingly thin armor, they were utterly uninspiring in service. Most ended up as photo-ops for Whermacht soldiers.