A new software framework for environmental simulation modeling is described. The framework facilitates fast, powerful model development by providing a system for implementing separate model elements as autonomous modules, which may then be tightly and flexibility integrated. The system is object-oriented, with integration of modules achieved through the sharing of common objects. Module autonomy is achieved by the use of generic messages passed between modules through shared objects. Shared objects represent concepts such as data, time, or sub-models. This facilitates effective model integration with no loss of speed as a result of the integration process. A large existing collection of modules, including IO, data representation and visualization, allows new models to be developed quickly with minimal attention to repetitive tasks. To date, the applications of the framework have been in the domains of hydrological, wildlife and ecosystem modeling. Experience has shown that the persistent merits of the framework include the data sharing/message passing approach, the generic conceptualization of modeling objects, and the body of modules assembled to date. The disadvantages are proving to be the dependence on a specific language and compiler. This hinders the utility of the framework for the broader model development community.