join.me - Instant screen sharing. Instant Aha!
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
WebEx - Cisco WebEx Web Conferencing, Online Meetings, Desktop Sharing, Video Conferencing
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.