Source: http://code.google.com/p/sipml5/

This is the world's first open source HTML5 SIP client (May 12, 2012) entirely written in JavaScript for integration in social networks (FaceBook, Twitter, Google+), online games, e-commerce sites... No extension, plugin or gateway is needed. The media stack relies on WebRTC.

The client can be used to connect to any SIP or IMS network from your preferred browser to make and receive audio/video calls and instant messages.

The protocol parsers (SIP, SDP...) are highly optimized using Ragel lookup tables and is suitable for embedded systems with limited memory and low computing power.
Features
Short but not exhaustive list of supported features:

  • Audio / Video call
  • Instant messaging
  • Presence
  • Call Hold / Resume
  • Explicit Call transfer
  • Multi-line and multi-account
  • Dual-tone multi-frequency signaling (DTMF) using SIP INFO

Note. sipML5 works on any web browser supporting WebRTC but we highly recommend using Google Chrome Canary 20.0.1127.0 or later for testing.