PocketSVG

https://github.com/pocketsvg/PocketSVG

Easily convert your SVG files into CGPaths, CAShapeLayers, UIBezierPaths, or NSBezierCurves. This makes it easy to create vector-based paths and shapes in your iOS or macOS apps.

Over 1000 GitHub stars, used in the Uber iOS apps.

The Amazing Audio Engine

http://theamazingaudioengine.com/

The Amazing Audio Engine is a sophisticated framework for iOS audio applications, allowing, among other things, real-time audio recording, processing, and mixing.

I helped build an audio sequencer module for The Amazing Audio Engine.

Note: This library has now been retired.

The Synthesis Toolkit in C++

https://github.com/thestk/stk

The Synthesis ToolKit in C++ (STK) is a set of open source audio signal processing and algorithmic synthesis classes written in the C++ programming language.

The STK was designed to facilitate rapid development of music synthesis and audio processing software, with an emphasis on cross-platform functionality, realtime control, ease of use, and educational example code.

I helped improve the STK’s support for iOS.