Portable networking and other low-level I/O, including sockets, timers, hostname resolution, socket iostreams, serial ports, file descriptors and Windows HANDLEs.
C++11-style atomic<>.
Context switching library.
Coroutine library.
(C++14) Coroutine library.
Shared memory, memory mapped files, process-shared mutexes, condition variables, containers and allocators.
Lockfree data structures.
Message Passing Interface library, for use in distributed-memory parallel application programming.
Portable C++ multi-threading. C++11, C++14.