Mahara is an open source Covid-19 tracing app made with usability and accessibility in mind. The official New Zealand tracing app is (from what I can see) completely closed source, and does not specify where and how user information is stored.
I designed Mahara to work completely offline, with no need for third-party servers and have everything stored locally on the device itself. Utilising the NFC reader and/or camera to scan QR codes, the usre has the option to check-in to different locations for their own personal records much like a diary. User information never leaves the device, and is encrypted using bcrypt for security.
The Figma design files for the app are available here for anyone to use freely under the GPLv3. I plan on making the underlying code GPLv3 as well and publishing it on my Sourcehut.