Brachymyrmex are some of the smallest ants in the world. They are found throughout the new world but are particularly diverse in the Neotropics. A few species, such as B. patagonicus pictured below, have spread to warmer regions around the world with human commerce.
Yes, Brachymyrmex and Oligomyrmex are some of smallest ant species. There are also Pyramica, Proceratium and Leptanilloides, then Leptanilla and other leptanillinae.