The GNU Gatekeeper is a free H.323 gatekeeper based on the OpenH323 project. You can use it to manage a Voice-over-IP network and let endpoints (e.g., Netmeeting) communicate through symbolic names. It also has an external interface for billing and other applications. It runs on a number of Unix versions (including Linux and Solaris) and Windows.
Noojee Receptionist for Asterisk provides a software-based interface for receptionists. It provides the ability to dispatch calls using a database of all staff and external parties or by phone or extension number. When looking up internal extensions, the status of each extension is displayed, saving the receptionist time as they no longer have to dial the number to determine if the party is available. When an extension is busy, the call can be placed into a "hold and transfer" mode that will automatically transfer the caller when the extension becomes available. It can also periodically inform the caller that the party is busy and gives the option to continue waiting, leave a voice message, or be put back through to the receptionist.
Yate is a next-generation telephony engine. While currently focused on Voice over Internet Protocol (VoIP) and PSTN, its power lies in its ability to be easily extended. It supports SIP, H.323, IAX, MGCP, Jingle, Jabber, E1, T1, analogic, robbed bit, ISDN PRI, BRI, and SS7. YateClient is an Instant Messenger and Voice application for Jabber/Jingle IM, SIP, H.323, and IAX VoIP protocols.
SafiWorkshop allows you to design, test, debug, and deploy advanced process flow applications (like IVRs) from a single, unified development environment. For database work, it includes a fully featured SQL query editor. SafiWorkshop also includes some Asterisk PBX specific features like an audio prompt editor.
Gammu (formerly known as MyGnokii2) is a cellular manager for various mobile phones/modems. It supports a wide variety of Nokia, Symbian, and AT devices (Siemens, Alcatel, Falcom, WaveCom, IPAQ, Samsung, SE, and others) over cables, infrared, or BlueTooth. It contains libraries with functions for ringtones, phonebook, SMS, logos, WAP, date/time, alarm, calls, and more (used by external applications like Wammu). It also includes a command line utility that can make many things (including backups) and an SMS gateway with full MySQL and PostgreSQL support from the PHP interface.
gnokii is a multisystem tool suite for mobile phones. It provides a library to communicate with a phone hiding the communication protocol. The library handles SMS, phonebook, calendar, phone calls, and other mobile phone capabilities. It supports Nokia-FBUS mobiles, AT-capable phones (most of the mobiles), as well as Symbian-based phones.
Linphone is an audio and video Internet phone with GTK+ and console interfaces. It uses the SIP protocol, and is compatible with most SIP clients and gateways. It can use various audio and video codecs such as Speex, GSM, G711, G722, ilbc, amr, Theora, H263-1998, MPEG4, H264, VP8, and snow.