Rubber Band Library is a high quality software library for audio time-stretching and pitch-shifting. It permits you to change the tempo and pitch of an audio stream or recording dynamically and independently of one another.
Dataquay is a free open source library that provides a C++ API for the Redland or Serd/Sord RDF libraries using Qt4/5 classes and containers.
Very simple sample app for Android using the Rubber Band Library
MiniBPM is a fixed-tempo BPM estimator for music audio, self-contained and implemented in a single C++ file.
Small C++ library wrapping various audio file read/write implementations
Very simple sample app for Android using the MiniBpm tempo estimator
Small C++ library wrapping various FFT implementations for some common audio processing use cases