Gradio

No JavaScript, no frontend knowledge required.

Apache 2.0, Python. Backed by Hugging Face (they acquired the company). The API is dead simple: define your function, specify input/output types, and Gradio generates the web interface. Supports text, images, audio, video, files, dataframes, and custom components. Share instantly via a temporary public URL or deploy permanently on Hugging Face Spaces for free.

Fully free. No paid tier for the library itself. Hugging Face Spaces offers free hosting with some compute limits; paid Spaces start at $7/month for dedicated hardware. Solo ML engineers: this is how you demo your work. Build a model, wrap it in Gradio, share the link. Takes 10 minutes. Small teams: use it for internal tools and stakeholder demos. Medium teams: build it into your ML workflow for model evaluation interfaces.

The catch: Gradio is built for demos and internal tools, not production apps. The generated UIs are functional but not customizable enough for customer-facing products. Performance degrades with concurrent users; it's running your Python function synchronously by default. For production ML serving, use a proper API (FastAPI + frontend) instead of a Gradio wrapper.