Sortd - Rated the #1 App for Gmail
OneTab - Whenever you find yourself with too many tabs, click the OneTab icon to convert all of your tabs into a list. When you need to access the tabs again, you can either restore them individually or all at once.
KanbanMail - A Kanban board for your emails.
Toby - Better Than Bookmarks
Drag for Gmail - Transform Gmail into organized To Do lists (like Trello)
Session Buddy - Manage Your Browser Sessions