This is one that allows you to measure speed in Kilometers per hour and meters per second simultaneously.
Now it is also possible to measure the distance traveled and the maximum speed reached.
All you have to do is grant access to your cell phone's GPS to the application.
It is a paid application, but Open Source.
This means anyone can see how it was made, redistribute it and release their own version.

The app was built using the QT 6 Framework: https://www.qt.io/
Its code is available on GitHub: https://github.com/ISSolucoes/velocimetro
Through this link you can understand how the application works and verify that there is no data collection by the developer.