Numerical modeling in the water sciences has been shifting from developing single or specific purpose-oriented tightly intertwined model applications to integrated model systems addressing more complex and interlinked geo-physical, -chemical and -biological processes across all strata of the critical zone geo-volume. This is a response to a number of important issues that span from preservation of legacy software, to a higher degree of development cost efficiency, to the realization that processes in one strata depend on others, to harmonizing software system usage, and to improving code provenance and repeatability of model runs. Consequently, a number of community modeling systems (CMS) have either been proposed or are being developed with individual communities typically taking the lead to develop a CMS for their constituency. While the development of CMS is a major step forward in trying to harmonize modeling efforts, chosen approaches vary with numerous efforts underway to arrive at a workable and functional CMS. This review seeks to provide an overview of these efforts, with a focus on those that address processes located in the critical zone, and tries to assess their degree of success based on some general criteria for the development of CMS.