AudioKit's free, feature-loaded synth is available for iPhone

Synth One is now a universal iOS app.

AudioKit Synth One was a minor breakthrough for mobile music making as a free, open source synthesizer that could compete with the heavyweights, but its iPad-only nature limited its audience. You'll be glad to hear, then, that AudioKit Pro has launched a universal version of the app that works with iPhones. It's the same professional-grade hybrid analog/FM poly synth as before, complete with LFOs, oscillators, sequencers and hundreds of presets. It's just crammed into a smaller screen area. You wouldn't want to use this for full-time music creation due to the limited room for controls, but this could be helpful for starting work on a track when you're nowhere near a studio.

You'll need at least an iPhone 6 for this version (the SE is just too small, unfortunately). However, it's truly free -- there are no ads or in-app purchases to sully the experience. AudioKit Pro is also rolling in a new bank from sound designer Francis Preve. If you've balked at the thought of paying $20 or more just to take music composition on the road, this might be worth a look.