Mixed Effects GENeralised REGression models
The megenreg packages implement the methodology described in the paper:
Crowther MJ. Extended multivariate generalised linear and non-linear mixed effects models. arXiv:1710.02223.
You can get the preprint here, which I recommend you read before trying out the accompanying software. The software is being constantly developed and improved. This page details the development of the package, both in terms of version histories and planned features to be added.