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.
CT Server is a Perl module that interfaces with Voicetronix computer telephony cards, giving developers a method of creating quick and creative computer telephony applications. A complete PBX is included as an example, which includes a Web interface for configuring and monitoring the PBX.
CapiSuite is an ISDN telecommunication suite providing easy-to-use telecommunication functions which can be controlled from Python scripts. It uses a CAPI-compatible driver for accessing the ISDN-hardware, so you'll need a CAPI-compatible driver. CapiSuite is distributed with two example scripts for call incoming handling and fax sending. They provide a multi-user answering machine with fax recognition, remote inquiry, and fax receiving/sending functions.
The CommuniGate Pro Community Edition provides a single address and identity for all forms of Internet communications. You can check your e-mail, chat with colleagues via Instant Messaging and VoIP, view multiple calendars (and other presence features), maintain address books, and view streaming RSS news feeds, all through the powerful Flash-based interface.
Ekiga (formely known as GnomeMeeting) is a soft phone, video conferencing, and instant messenger application for use over the Internet. It supports HD sound quality and video up to DVD size and quality. It is interoperable with many other standards compliant software, hardware, and service providers as it uses both of the major telephony standards, SIP and H.323.