I maintain a list of open source UIs built on top of OpenAI API to explore unique features and integrations that others have developed: https://github.com/itsuka-dev/awesome-chatgpt-ui. Web version, which has more information: https://atorie.xyz/crafts/plurality

In addition to the usual speech synthesis/recognition and embedding/vector search features, there are also:

- Node layout

- Multiple LLMs and parallel output

- 3D avatar

- Selection + custom context menu (for extensions)

- Native app integration such as Siri and Calendar (for Shortcut in Apple ecosystem)

- etc. (I'm sure there are many other interesting UIs and features that I missed.)