Folly
Folly (Facebook Open Source Library) is a C++ library developed by Meta (formerly Facebook) that provides a collection of reusable components for building high-performance, scalable systems. It includes utilities for concurrency, memory management, data structures, and asynchronous programming, designed to complement the C++ Standard Library with Facebook's production-tested optimizations. The library emphasizes efficiency, reliability, and compatibility with modern C++ standards.
Developers should learn and use Folly when building performance-critical C++ applications, such as backend services, distributed systems, or low-latency systems, where standard library components may not suffice. It is particularly valuable for projects requiring advanced concurrency models (e.g., fibers), custom memory allocation, or optimized data structures like string handling and hashing, as it offers battle-tested solutions from Facebook's large-scale infrastructure.