Asterisk is described as 'is free software that transforms a computer into a communication server. Asterisk lets you build applications like PBX, VoIP gateway, IVR and ACD' and is an app in the Social & Communications category. There are more than 25 alternatives to Asterisk for a variety of platforms, including Linux, Windows, Mac, Online / Web-based and Android. The best alternative is 3CX Phone System, which is free. Other great apps like Asterisk are Wazo (Free, Open Source), FreeSWITCH (Free, Open Source), FusionPBX (Free, Open Source) and Kamailio (Free, Open Source).
OpenSIPS (Open SIP Server) is a mature Open Source implementation of a SIP server. OpenSIPS is more than a SIP proxy/router as it includes application-level functionalities. OpenSIPS, as a SIP server, is the core component of any SIP-based VoIP solution.
Ozeki Phone System XE is a Software PBX telephony platform for Windows. Ozeki enables your applications to connect PBX and access IVR, Webphone, SMS sending, 3D video calls and other functionalities. It makes possible to use PHP VOIP, .
The MiRTA PBX is an interface written in PHP using Mysql as backend to manage a multitenant PBX built over the Asterisk Open Source PBX. An easy to use interface allows you to manage one or more Asterisk PBX in a multi tenant, load sharing and high availability configuration.
uContact is an All in One contact center solution that includes ACD, recording, dialers (preview, power and predictive), Social Networks, CRM, WFM, quality, call reporting, live monitoring, IVR, SMS, Web Chat with audio and video, Gamification, etc.