TidyHQ - Organization management tool to support membership, subscriptions, event planning, and outreach.
Shift - Shift is the ultimate email client for managing Mail, Calendar, Drive, Slack, Asana, Jira, Evernote, and all your other favourite apps
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Mia for Gmail - A desktop email client for your Mac, without a browser !
Membee - Membee is web-based membership management software.
Mailplane - Mailplane is the best way to use Gmail on your Mac. Use an unlimited number of accounts, get new mail notifications, use plug-ins and much much more.