A free program for Android, by DotDotDog.

This free Bubble Level app for Android is a must-have app for anyone who needs to know the angle of the surface. With this, you will be able to level things like a table or wall. 

You can also use it to measure the angle of any surface. It is very simple to use, and you don’t need to use any other tools. Just put your Android device against the wall or object you want to measure, and you can start measuring.

If you want to know the angle of the surface you are on, this is the best tool to use.