CleverTap - CleverTap offers blazing fast analytics, powerful real-time segmentation, multi-channel messaging, A/B testing and personalization in one unified solution.
Tragofone - White-label VoIP Softphone with WebRTC and Auto-provisioning
Apple App Analytics - Apple's very own iTunes Connect App Analytics
PhonerLite - PhonerLite enables your PC to use it for internet telephony (VoIP , Voice over IP, SIP).
Callcounter.eu - Callcounter gathers API usage data and gives you insight in trends, slow parts and errors.
tSIP - tomeko.net/software: SIP client for Windows.