Gemini is the model family.

Antigravity is their agentic coding app / IDE. There is two products, one is chat-only the other is more standard IDE.

Google AI Studio is a consumer/developer playground with a in-browser IDE meant for prototypes or demos, there is a gallery of demos etc. Easily shared, easy key access.

Vertex is the AI offering from the GCP side of the company, that is going to target more enterprise or business solutions (scaling, data governance, security, production deployents, etc)