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.
GNU SIP Witch is a secure peer-to-peer VoIP server. Calls can be made even behind NAT firewalls, and without requiring service providers. SIP Witch can be used on the desktop to create bottom-up secure calling networks and as a free software alternative to Skype. It can also be used as a stand-alone SIP-based office telephone server, or to create secure VoIP networks for an existing IP-PBX such as Asterisk, FreeSWITCH, or Yate.
GYach Enhanced is a feature-rich, improved version of the original Gyach. It is the first Yahoo! client for Linux with voice chat capabilities. It offers almost all of the features you would expect to find in the official Windows Yahoo! client. The program offers support for chat, conferences, buddy lists, and My Yahoo content. In addition, Gyach Enhanced offers many features not available in the official Yahoo! clients for Windows, Mac, and Linux. Webcam support is under development and planned for the future. Unlike the original Gyach, GYach Enhanced is designed for Linux only.
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.
Gemeinschaft is a PBX based on Asterisk, MySQL, Apache, and PHP, and designed for high availability and clustering. It provides automatic provisioning for mass deployment, and can handle over 10,000 users. Administration is done via shell scripts or a Web GUI. Hot-desking and mobility are supported. German voice prompts are included. There is a standards-compliant Web GUI with internationalization (and German and English translations). Outbound and inbound routing with full PCRE support is included.