4PSA VoipNow is PBX software for service providers and enterprises. Easy to use and deploy, it can run on x86 or PowerPC based servers and delivers advanced IP telephony services. It can be deployed in various working scenarios to provide hosted VoIP services in high availability xSP environments, advanced call center services, or enterprise telephony in organizations of all sizes. A free Express version is available.
ADM (Asterisk Desktop Manager) aims to integrate your desktop with the Asterisk PBX and hardware IP phone by providing some useful features such as automatic on-call volume reduction, one click dialing (from the clipboard), CRM integration via a browser popup, BlueTooth presence detection and automatic call redirection when you walk out of the office, and transfer of the current call from the desktop.
AgileVoice provides features for running VoIP businesses, including broadband residential and business phone, PC to phone, wholesale (termination/origination), traffic exchange, IP centrex, calling cards, and more. It was designed with carrier grade customers in mind. As such, it scales from many Asterisk systems down to a single all-in-one system.
Asterisk is a hybrid TDM and packet voice PBX (Private Branch eXchange) and IVR platform with ACD functionality. It acts as middleware between the Internet (IAX, SIP, MGCP, Skinny, H.323), telephony channels (like Zaptel, T1, PRI, E1, FXO, FXS, VoIP, VoFR, ISDN, modems, Internet Phone Jack, etc.), and applications (like voice-mail, conferencing, directories, MP3 players, intercoms, etc.). It has many advanced features such as a codec translation API. The base distribution includes several channel backends, as well as applications. However, the beauty of Asterisk is its ability to be extended using its APIs, dynamic module loader, and AGI scripting interface. End users can even write their own applications that run on the system in C or any scripting language of their choice.