I don't remember exactly (don't have it handy right now), but when I was looking, I tried searching the app store for digital protractor once and wasn't very successful. Searching google for the same term then turned up an alternate search term called "inclinometer" which was much more helpful in the app store. Also can search for bubble level.
Just be sure to find one that you can calibrate easily. Whatever one I have, I can set my I-pad on my drill press bed or track or anything and just tap an icon to calibrate to zero (bubble centered) and then when tilted it moves the bubble like a level, but also displays the digital read out in degrees. I think I can even turn it on an edge to measure that way too.
