WebAssembly Wasm
Portable binary instruction format for a stack-based VM — runs in all modern browsers, also server-side via Wasmtime/Wasmer.
Predecessor: asm.js (Mozilla, 2013). Wasm 1.0 approved by W3C in 2019. Lets C/C++/Rust/Go/Zig/C# compile to web-runnable code. Performance close to native. WASI (WebAssembly System Interface) gives Wasm OS APIs outside the browser → runs as "Docker but smaller" at the cloud edge. Fastly Compute, Cloudflare Workers use Wasm. Spin (Fermyon) builds serverless on top.