WASI (WebAssembly System Interface) breaks WebAssembly out of the browser, letting compiled modules interact directly with operating systems. Historically, Wasm was confined to web tasks, but WASI provides the standard bridge for file access, networking, and more, turning Wasm into a truly portable runtime.

This matters because it enables a 'write once, run anywhere' model for performance-critical code. Developers can build server-side applications, CLI tools, and IoT software in languages like Rust or Go, then deploy them anywhere a WASI-compliant runtime exists, with built-in sandboxing and capability-based security.

The ecosystem is maturing with runtimes like Wasmtime and Wasmer. While tooling is still evolving, WASI's modular interfaces—from file I/O to networking—promise to reshape cloud and edge computing. The push comes from the Bytecode Alliance, aiming to standardize Wasm beyond the web.