This is the application we use for our end-to-end tests, and for reproducing bugs via CodeSandbox.
From the react-admin repository:
# install the dependencies for the monorepo
make install
# run the app in extended watch mode (reloads when a change is detected in the app code and in the packages code)
make run-simple
And then browse to http://localhost:8080/.
The credentials are login/password