TanStack Start is a meta-framework built on TanStack Router and powered by Vite that offers a client-first approach to full-stack development. Key features include file-based routing with end-to-end type safety, server functions for secure server-side operations, isomorphic code execution by default, and flexible rendering modes (SSR, client-side, or hybrid). The framework emphasizes component collocation, allowing data fetching, validation, and mutations in the same component. While it lacks React Server Components support currently, its selective server-side rendering and natural development experience make it an attractive alternative to Next.js for interactive applications.