All this classes provide communication and syncronizzations tool for threads and processes as: semaphore, critical sections, shared memories and so on. They provide some supports tools as: string wrapper, MD5 alghoritm, hash and vector managing (perl like) and so on.
AP is very important in a Linux system because it is a multi-thread / multi-process operative system. The communications between thread is very different from processes communication because the first works in the same memory space and all instances are visible to all classes. The second works in different memory space and we have to use kernel objects (POSIX) to exchange data and information.
AP provides a trasparent platform to exchange data and messages for processes-to-processes, threads-to-threads and processes-to threads communications.