go install golang.org/x/build/cmd/coordinator && coordinator --mode=dev --env=dev
to start a server on https://localhost:8119. Proceed past the TLS warning and you should get the homepage. Some features won't work when running locally, but you should be able to view the homepage and the builders page and do basic sanity checks.
Render the "Trybot Status" page locally
To view/modify the "Trybot Status" page locally, you can build the coordinator
go install -tags=dev golang.org/x/build/cmd/coordinator
Then start the coordinator and visit https://localhost:8119/try-dev in your browser. You should see a trybot status page with some example data.