Vakarta is a website that can also be an app.
You need to be vaccinated more than once, but not every day. Therefore, it makes no sense to take up tens or hundreds of megabytes of your smartphone. In addition, modern technologies allow you to create PWA (Progressive Web Applications) that take up very little space and are fully perceived by devices.
Vakarta is already available on the Google Play Store, but some vaccinations (for example, against COVID-19) are limited there due to Google's international policies:
Google Play
In any case, for iPhone and Android you can install the Vakarta app in a couple of clicks. Follow the simple instructions for your browser.
Vaccination is easy.
Create a personal vaccination calendar