These are 3 apps that can help you make music and sounds.
Sonic Synth is vary capable FM synthesiser app with 3 oscillators. Every oscillator is independent and can generate 4 wave forms. Has reverb, wave modulation, detune, tone offset.

Jack the beat maker is pocket size drum machine, perfect for making beats.
You can record live with the drum pads and even add simple bass line to the beat. Exports to WAVE and MIDI. The app has 2 drum kit sounds with 12 samples in each.
Frequency Sound Generator is a simple wave form sound generator and oscillator. It is easy to use tool so you can create high variety of sounds and signals in just few seconds. There 3 oscillators in this app that can play together.