Skype for Slack - Move your slack discussions to a group skype call
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
Aircall Now - Make voice calls inside Intercom Messenger 📞💬
Bigtent - BigTent is a web-based organization and communication portal for groups.
Calls on Slack - Make voice calls in Slack
Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.