Asterisk alternatives

Asterisk
An open source telephony switching and private branch exchange service for Linux. Information on downloading, installation of and support for the product. 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.
Asterisk alternatives are:
3CX, ShoreTel, Twilio