The FrequencyModulation app is a free Android app for making analog synth sounds. This app has two main menus: a carrier and modulator. They both have a frequency, detune, attack, gain and release slider and they can both be selected to a square, sine or triangle waveform. The app has a trigger button to play the sound. This is in my opinion a tutoring app as you can learn more than you can produce, but as it was built by just a single person, it surely is great. It is like a synthesizer for sampling music and for making ideas for implementing in songs. You can never have too much synthesizers on your phone or tablet and each makes a different sound due to its unique user interface. This app is especially good because it shows you what you are doing with the sound and because it has a really reliable interface. This app will work on screen any size and on many outdated phones as well. The FrequencyModulator app can be used for teaching as well so to show students or pupils how frequencies look like and how soundwaves differ among each other.