Outlook Google Calendar Sync - Offers calendar synchronisation between Outlook and Google, including attendees and reminders.
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
gSyncit - gSyncit Outlook Cloud Synchronizer. Outlook Calendar, Contact, Task, Note Synchronizer supporting Google, Toodledo, Evernote, Informant, iCloud, AOL, Yahoo, Synology, Fruux, Memotoo and CalDav/CardDav services.
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
EteSync - Secure, end-to-end encrypted and journaled personal information synchronization.
MailClark - The Slack bot for external communications