Deno is a modern runtime for JavaScript and TypeScript that fixes many of Node.js's design decisions. It's fundamentally similar (V8 engine, async/await) but differs in key ways: no npm/node_modules (URLs for imports), TypeScript out-of-the-box (no separate transpiler), and explicit permissions (security by default). You use Deno to build backend APIs (with Oak or Hono), CLIs, automation scripts, and microservices. Code is simpler than Node—no build steps, no dependency hell—making rapid iteration fast.