Documentation is at docs/guide/README.md.
common
config/ contains shared configurations
mail/ contains view files for e-mails
models/ contains model classes used in both backend and frontend
tests/ contains tests for common classes
components
phpclient.php/ contains shared rabbitmq class
console
config/ contains console configurations
controllers/ contains console controllers (commands)
migrations/ contains database migrations
models/ contains console-specific model classes
runtime/ contains files generated during runtime
backend
assets/ contains application assets such as JavaScript and CSS
config/ contains backend configurations
controllers/ contains Web controller classes
models/ contains backend-specific model classes
runtime/ contains files generated during runtime
tests/ contains tests for backend application
views/ contains view files for the Web application
web/ contains the entry script and Web resources
frontend
assets/ contains application assets such as JavaScript and CSS
config/ contains frontend configurations
controllers/ contains Web controller classes
models/ contains frontend-specific model classes
runtime/ contains files generated during runtime
tests/ contains tests for frontend application
views/ contains view files for the Web application
web/ contains the entry script and Web resources
widgets/ contains frontend widgets
vendor/ contains dependent 3rd-party packages
environments/ contains environment-based overrides