What happened to the US Apple/Google app?
It up to countries and states to build apps on those APIs.
* https://9to5mac.com/2020/05/21/covid-19-exposure-notificatio...
* https://www.wired.com/story/covid-19-contact-tracing-app-fra...
TL;DR: Hardly any.
Edit: Whoops, I am out of date, I thought 13.5 was not out yet! Apparently it is, and then some.
> To implement its contact tracing functionality, Immuni leverages the Apple and Google Exposure Notification framework (see Apple’s documentation and Google’s documentation). This allows Immuni to overcome certain technical limitations, thus being more reliable than otherwise would be possible.