Right Inbox - schedule emails, set up recurring emails, set reminders and follow-ups to emails

Grammarly - Spelling and grammar will be vetted on Gmail, Facebook, Twitter, LinkedIn... nearly everywhere you write on the web

Gmail Notes - add annotations or notes to your emails

Convert Google Docs to Gmail - you can convert a Google Doc into a Gmail with 1 click and never lose any of your formatting.

Gmelius - Make your inbox smarter: Send later, snooze, free email tracking, shared templates, kanban to-do list, email notes and more