Asterisk is a software implementation of a telephone private branch exchange (PBX); it was created in 1999 by Mark Spencer of Digium. Like any PBX, it allows attached telephones to make calls to one another, and to connect to other telephone services, such as the public switched telephone network (PSTN) and Voice over Internet Protocol (VoIP) services. Its name comes from the asterisk symbol:
Asterisk is like a box of Legos for people who want to create communications applications. It includes all the building blocks needed to create a PBX, an IVR system, a conference bridge and virtually any other communications app you can imagine.
Banana Pi is a single-board computer built with ARM Cortex-A7 Dual-core (Allwinner A20 based) CPU and Mali400MP2 GPU, and open source software, Banana Pi can serve as a platform to make lots of applications for different purposes.