The second version of the natstrat package, which now allows balancing covariates for multiple different comparisons at the same time as well as any number of treatment groups. This version also adds the ability to choose between independent multinomial sampling for each unit and fixed sample size dependent sampling for the randomized rounding algorithm. This was used for the submitted manuscript "Using Natural Strata When Examining Unmeasured Biases in an Observational Study of Neurological Side Effects of Antibiotics" (Brumberg, Ellis, Small, Hennessy, and Rosenbaum; 2021).