The C++ Portable Types Library (PTypes) is a simple alternative to the STL that includes multithreading and networking. It defines dynamic strings, character sets, variants, lists and other basic data types along with threads, synchronization primitives and IP sockets. It is portable across modern Unix and Windows systems and includes a sample HTTP daemon showing the full power of the library.
HappyHTTP is a simple C++ library for issuing HTTP requests and processing responses. It is simple to integrate: just drop in the .h and .cpp files. It has an easy-to-use interface, non-blocking operation (suitable for use in game update loops), and pipelining support (you can issue multiple requests without waiting for responses).