While there is no contact tracing app for the entire world or nation, many states have their own contact tracing app. These contact tracing apps can be used to help automatically notify you if you get in contact with some one who has tested positive. These apps could definitely be useful to flattening the curve if more people know about this and download them.
How they work:
"Public health authorities around the world are building apps that use the Exposure Notifications System to help their contact tracing efforts. On Android, you can find the app for your area, if available, on Google Play. Android users will also receive a notification from the Play Store, if their state has made Exposure Notifications available.
If you have an iPhone, opt-in to Exposure Notifications in your device settings (coming soon).
Once you opt-in to the notification system, the Exposure Notifications System will generate a random ID for your device. To help ensure these random IDs can’t be used to identify you or your location, they change every 10-20 minutes.
Your phone and the phones around you will work in the background to exchange these privacy-preserving random IDs via Bluetooth. You do not need to have the app open for this process to take place.
Your phone periodically checks all the random IDs associated with positive COVID-19 cases against its own list.
If there’s a match, you will receive a COVID-19 exposure notification, with further instructions from your public health authority on how to keep you and the people around you safe." - Google
"We understand that the success of this approach depends on people feeling confident that their private information is protected. The Exposure Notifications System was built with your privacy and security central to the design. Your identity is not shared with other users, Google, or Apple." - Google