Boost
You have to be wary of using third-party libraries, especially when there's so much good stuff in the core library! But if you must, consider constraining it to a subsystem rather than letting it creep throughout the codebase.
- Boost.Asio
- Boost.Signals2
- Boost.Thread
Boost.Test
- Should I become proficient in STL before learning Boost?
- Comparing C++ and Boost