Sortd - Rated the #1 App for Gmail
Send to Dropbox - Email attachments to a Dropbox folder
KanbanMail - A Kanban board for your emails.
Get My Receipts by cloudHQ - Organize your receipts in one click
Drag for Gmail - Transform Gmail into organized To Do lists (like Trello)
OneBox.io - Sync e-mail attachments to GDrive, Dropbox, Box, or OneDrive