merlin stands for Mixed Effects Regression for LInear, Non-linear and user-defined models. merlin can do a lot of things, from simple stuff like fitting a linear regression or a Weibull survival model, to a three-level logistic mixed effects model, or a multivariate joint model of multiple longitudinal outcomes (of different types) and a recurrent event and survival with non-linear effects… the list is rather endless. merlin can do things you or I haven’t even thought of yet.