The **udid** module provides a simple way for an application to obtain a stable, unique identifier for the machine it’s running on. It does this by trying several strategies—hashing the user’s SSH public key, generating and persisting a UUID in ~/.udid, and, in browsers, using a tab‑counting fallback—so it works across Node.js and client‑side environments. It’s aimed at developers building distributed systems or any app that needs a reliable per‑device identifier without requiring platform‑specific APIs.