Skype for Slack - Move your slack discussions to a group skype call
Zoho Meeting - Free video conferencing, online meeting, desktop sharing solution from Zoho.
Calls on Slack - Make voice calls in Slack
FileFlex - FileFlex: Access Share Stream developed and published by Qnext.
CallKite - Your website’s video call center in just one click.
Airtime - Hang out with group video, share music & videos