Sortd - Rated the #1 App for Gmail
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Drag for Gmail - Transform Gmail into organized To Do lists (like Trello)
Roundcube - Web-based IMAP email client
Get My Receipts by cloudHQ - Organize your receipts in one click
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.