Skype for Slack - Move your slack discussions to a group skype call
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Aircall Now - Make voice calls inside Intercom Messenger 📞💬
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
Calls on Slack - Make voice calls in Slack
TidyHQ - Organization management tool to support membership, subscriptions, event planning, and outreach.