Read more about Toolbelt 4.0 plugins here.
This CLI comes built into the Heroku CLI. https://cli.heroku.com
$ heroku status === Heroku Status Development: No known issues at this time. Production: No known issues at this time.
or, if there were a real incident...
$ heroku status === Heroku Status Development: Yellow Production: Yellow === Increased Platform Latency 7:04:22 PM UTC 7:04:22 PM UTC (42 minutes ago) [Issue] We are experiencing a network connectivity issue with our upstream provider. We will post another update as to the status in an hour if not sooner.