The Tok, common on the milsurp curio and relic market, was the standard Soviet handgun for generations and while the M57 variant is based on it, it’s a little different at the same time.
Designed to replace the Tsarist-era M1895 Nagant revolver, Fedor Tokarev’s TT30/33 pistol was very similar to John Browning’s single-action handguns of the early 1900s and was used by the Soviets until the 9x18mm Makarov came on the scene in the 1950s. However, a number of Communist countries needed new handguns after WWII and in the interest of International Solidarity, Moscow soon passed on the design to allies in Poland, Romanian, and Yugoslavia, among others. Many of these second-tier makers incorporated changes to the base design and Zastava was no different, modifying their production example as the M57.
While still chambered in 7.62x25mm, there are some M57s chambered in 9mm (the M70) and, as Tim with the Military Arms Channel points about in the above while comparing the Yugo to Soviet and Polish Toks, the M57 has a longer grip and some other small tweaks.
The more you know…