nlmxr is an open-source R package for population PK/PD modelling developped by Wenping Wang and Yuan Xiong, in collaboration with Occams (Rik Schoemaker and Justin Wilkins).
Christian, at that time as an Exprimo member, has built a bunch of simulated datasets from a large panel of PK and PK/PD models and some of them were used to challenge nlmxr.