On old FreeBSD versions and on the latest OpenBSD (5.4), the multiprocessing module is not available because POSIX semaphores are not supported by the OS. See issues #5725 and #10348 to use SysV semaphores. #10348 was closed because "implementing SysV semaphores would be a step backwards, plus the API is a real pain" (wrote Charles-François Natali).

Would it be possible to make concurrent.futures dependency optional? In Trollius project (port of asyncio on Python 2), I implemented a very simple synchronous executor used by default as a fallback when concurrent.futures is not available (Trollius uses futures, backport of concurrent.futures for Python 2).

Attached patch is the synchronous executor adapted again on asyncio.

asyncio.executor.Future (when concurrent.futures is missing) is the simplest class and has a different API than concurrent.futures.Future. It is directly created with known result (value or exeption).