1. GNU Bayonne
GNU Bayonne, the telephony server of GNU Telephony and the GNU project, offers free, scalable, media independent software environment for development and deployment of telephony solutions for use with current and next generation telephone networks.
The OpenH323 project provides full featured, interoperable, Open Source implementation of the ITU H.323 teleconferencing protocol that can be used by personal developers and commercial users without charge.
TkPhone is a personal Phonebook to store and call the phone numbers of your private life. Numbers are stored in a $HOME/.tkphone subdir chmod'ed as 0700, so that noone can access them.