underscore-contrib is an extension library for Underscore.js, providing additional functional programming utilities that are too specialized or experimental for inclusion in the core Underscore library. It's designed for JavaScript developers who want to expand Underscore's capabilities with niche functions, serve as a proving ground for potential Underscore features, or explore advanced concepts like monads, currying, and laziness. The library is modular, allowing developers to include only the specific sub-libraries they need.