The unique 1794 dollar struck in copper from the regular dies. It is probably the second dollar coin struck at the U.S. Mint. The first, also struck in copper, is from a different obverse die without stars J18/P27.
Although it is the sharpest example of a 1794 dollar in existence, it shows the same weakness on the left side of the obverse and reverse caused by the dies being slightly out of parallel.
The pedigree of this famous coin dates back into numismatic antiquity. It is ex Haines (Bangs & Company 1/1863), McCoy (Woodward 5/1864), Levick (Woodward 10/1864), Levick (Bangs & Company 4/1865), Ely (Woodward 1/1884), Parmelee (New York Coin & Stamp 6/1890), Brand (1899 Journal #20691), Davis-Graves (Stacks 4/1954), Stacks, Smithsonian.
Judd and Pollock mention that electrotype copies exist.
Here is a second image of the piece.
Photos courtesy of the National Numismatic Collection of the Smithsonian Institution.