The best open source alternative to Google Fit is Open mHealth. If that doesn't suit you, our users have ranked more than 25 alternatives to Google Fit and seven of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Google Fit are OpenTracks (Free, Open Source), FitoTrack (Free, Open Source), ForRunners (Free, Open Source) and AAT (Free, Open Source).
Open architecture is software with source code that is freely available to developers to promote cooperation and interoperability. This means developers can more quickly and effectively work together to create optimized mHealth applications.
FitoTrack is a mobile app for logging and viewing your workouts. Whether you’re running, cycling or hiking, FitoTrack will show you the most important information, with detailed charts and statistics. It is open-source and completely ad-free.
HealthBox is a privacy respecting, encrypted, open source health data management system that makes it easy for applications, devices, and information sources to store information in a single, easy to access place.