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