MacOS X and Darwin
MacOS X is Apple Computer Inc's operating system, powered by a BSD subsystem called Darwin.
spc.

Open standards based SIP VoIP technologies available on MacOSX
- Asterisk - the open source PBX and multi-protocol VoIP server
- Blink - A fully featured SIP client for MacOSX (GPLv3) with support for IM, File Transfer and Desktop Sharing based on MSRP
- REMWAVE - A SIP client for MacOSX (GPLv3) geared towards ITSPs
- iaxComm - the open source IAX softphone
- ZoIPer - Multiplatform IAX soft phone (universal binary) (formerly Idefisk)
- JackenIAX - IAX Soft Phone for Mac OS X.
- LoudHush - nagware IAX softphone for OS X
- SJphone - SJlabs' H.323 and SIP softphone
- Telephone - the open source SIP softphone written in Objective-C/Cocoa
- VDK - Voip Development Kit - the cross-platform, c++ framework to create VoIP applications in a breeze.
- X-Lite - Xten's SIP softphone (note: crashes after every call under Intel, no plans to fix)
- Xmeeting - H323/SIP Audio Video Max OSX client , universal binairies.
- VoixManager Is an an IAX/IAX2 switchboard call manager for Operators and Receptionists, is able to manage and display information about your Asterisk PBX activity in real time. Has been thought with simplicity in mind, all feature needed by the attendant, fast and easy usable, with the minimum configurations, just fill the phone and manager login information and play.