Moonshine Voice is an open-source AI toolkit for building real-time voice agents and applications with on-device speech-to-text, text-to-speech, and voice cloning capabilities. The system emphasizes privacy, low latency, and offline operation through a cross-platform C++ core with language bindings for Python, Swift, Android, and WebAssembly. It includes optimized models for various platforms (from microcontrollers to desktops), multilingual grapheme-to-phoneme conversion, speaker diarization, and embedding-based phrase matching. The architecture features modular components for audio processing, model inference, and language-specific rules, with examples demonstrating microphone transcription, streaming TTS, agent workflows, and embedded deployments on RP2350 microcontrollers.