Elastix is a software appliance that integrates the best tools available for Asterisk-based PBXs into a single, easy-to-use interface. It also adds its own set of utilities and allows for the creation of third party modules. The goals of Elastix are reliability, modularity, and ease-of-use. It also features strong reporting capabilities.
Encours.org is a teleconferencing system that works directly in your Web browser. It has shared slides that are visible to all, an integrated audio system with recording, "laser" pointers for lecturers, video replays of the presentation, and a chat interface with the audience. It can be connected to a phone server.
The Taridium ipbx is a complete software-based VoIP PBX system that replaces a traditional proprietary hardware PBX. It runs on Linux without the need for extra software licenses, and is based on the SIP standard. It supports many phones and is available for free in a 5 user version.