Chrono is organized in modules.

Each module consists in additional libraries that can be optionally used to expand the features of Chrono, depending on users needs.

This allows to:

reduce the number of dependencies to the minimum, requiring only those strictly needed by the specific user;
have smaller size libraries, instead of a big ones;
have a better isolation during the development

Each module can be enabled/disabled through the corresponding ENABLE_MODULE_XXX in the CMake configuration.

The picture below illustrates how modules can depend on external libraries, whereas the core system of Chrono depends on the underlying operating system only.