Bayesian modellers are typically scientists and Stan probably has more indirect than direct users. For example, rstanarm and BRMS are both R regression packages

Bayesian modellers are typically scientists and Stan probably has more indirect than direct users. For example, rstanarm and BRMS are both R regression packages which use Stan which are wildly popular in Bayesian circles. They enable hierarchical Bayesian modelling which can be used to perform a very flexible kind of regression which allows the integration of lots of prior information, and better quantification of uncertainties than previous alternatives.