Xcode - Xcode is Apple’s powerful integrated development environment for creating great apps for Mac, iPhone, and iPad. Xcode 4 includes the Xcode IDE, instruments, iOS Simulator, and the latest Mac OS X and iOS SDKs.
Tragofone - White-label VoIP Softphone with WebRTC and Auto-provisioning
Android Studio - Android development environment based on IntelliJ IDEA
PhonerLite - PhonerLite enables your PC to use it for internet telephony (VoIP , Voice over IP, SIP).
Adobe AIR - Adobe® AIR® runtime enables developers to package the same code into native apps for Windows and Mac OS desktops, iPhone, iPad, Kindle Fire, Nook Tablet & Android. Buy now.
tSIP - tomeko.net/software: SIP client for Windows.