Fay focuses on practical end-user digital human applications and provides complete source code for those implementations. The framework can work with different digital human technologies and large language models, while making it easy to swap components such as TTS and ASR. It exposes a comprehensive set of interfaces for microcontrollers, apps, websites, large displays, and third-party business systems.

The README highlights capabilities such as flexible matching of digital human models, OpenAI-compatible large language models, ASR and TTS models; automatic broadcasting modes for virtual teachers, virtual hosts, and news presenters; support for many kinds of terminals; and text interaction, voice interaction, digital human control, management, automatic broadcast, and intent interfaces.