Only a few states have released them. Washington State people have been working on an app for a while; commoncircle.us seems to be their website, they have a github site that hasn't had a checkin for a couple of months. Is this effort dead? Their twitter account has nothing since July. Why isn't there an app available or any discussion?
Overview article of the US situation: https://gazette.com/health/people-proving-the-weakest-link-for-covid-tracking-apps/article_42a267c4-2aaf-11eb-85d8-cf1d8cde5661.html
Salon.com https://www.salon.com/2020/11/20/people-are-proving-to-be-the-weakest-link-for-apps-tracking-covid-exposure_partner/
UW engineering presentation about the effort by prof. Stefano Tessaro (Oct 2020) https://www.youtube.com/watch?v=geAIEwBOSRY&feature=emb_logo&ab_channel=UWVideo