fs-monkey cleverly intercepts Node.js's core fs module functions using monkey patching. This allows developers to modify or extend standard file system behavior without directly altering core modules. Common uses include virtualization, sandboxing, and custom file system implementations for testing or specific application needs. It offers a way to seamlessly integrate custom file system logic while maintaining the familiar fs API surface. Be cautious when using in production environments as modifying built-ins can have unforeseen consequences.