The site Rt.live is a tracker of how fast COVID-19 is spreading in each state updated daily. You can compare the current rates to yesterday, last week, 2, 3 and 4 weeks ago. The site also displays the Rt rate per state over time. I have not found another site that is looking at COVID-19 this way.
The site was created by Instagram founders Kevin Systrom and Mike Krieger, who have teamed up to launch their first product together since leaving Facebook. They (and their team) have developed an interesting statistical model. You need more that a basic understanding of statistics and programing to really understand how they have built their model. I’m not 100% in agreement with their model, but I haven’t been able to come up with an improvement.
Rt is the effective reproduction rate of the virus calculated for each locale. It lets us estimate how many secondary infections are likely to occur from a single infection in a specific area. Values over 1.0 mean we should expect more cases in that area, values under 1.0 mean we should expect fewer. You can download how they estimate Rt. They even share the code they wrote to manipulate the data.
The site is at https://rt.live