VoiceOne

Asterisk   (Compare Project)

Mostly written in C

License: gpl

blue.box project   (Compare Project)

Mostly written in PHP

License: mozilla_public_1_1

A2Billing   (Compare Project)

License: gpl

XiVO Solutions   (Compare Project)

Mostly written in Scala

License: gpl3, lgpl3

Elastix   (Compare Project)

Mostly written in PHP

License: AFL1-1, gpl

FreeSWITCH   (Compare Project)

Mostly written in C

License: AFL1-1, Apache_License_1_0, apache_2, apple_open_source, cecill-v2_1, computer_associates_trusted, copyheart, CC-BY-NC-ND-3-0-deleted, creative_commons_by_3_0_unported, dbad-license, OpenSSL_License, ROOT_License, ddmenu

Kazoo Platform   (Compare Project)

Mostly written in Erlang

License: mozilla_public_1_1

sipXcom   (Compare Project)

Mostly written in C

License: AGPL3_or_later

Chan-SCCP channel driver for Asterisk   (Compare Project)

Mostly written in C

License: GNU_General_Public_License_1_0

Gemeinschaft (by Amooma), later known as GS3   (Compare Project)

Mostly written in PHP

License: gpl