Automatic Speech Recognition: Apple Speech API and CMU Sphinx/Pocket Sphinx.
Speech Synthesis: Apple Speech Synthesis Framework and CMU Flite/Flite+HTS.
Audio Playback: Standalone and with speech recognition.
Audio Recording: Standalone and with speech recognition.
Acoustic Echo Cancellation: Device and software based.
Voice Activity Detection: During audio playback and speech recognition.
iOS Device Audio Configuration & Event Detection.