MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.
ClickMeeting - Collaborate with partners and clients using ClickMeeting professional web conferencing software. Try it now, FREE!
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Zoom - Equip your team with tools designed to collaborate, connect, and engage with teammates and customers, no matter where you’re located, all in one platform.
tSIP - tomeko.net/software: SIP client for Windows.
BigBlueButton - Engage Your Online Students. BigBlueButton is a web conferencing system designed for online learning.