Gmail Add-ons are a New way to work with Business Apps
Google has a number of features built into Gmail including unique themes, different layouts and an entire Labs section with a dozen different experimental options to help you customize your Gmail experience. To expand on this, the company has just launched what they’re calling Gmail Add-ons as a new way to work with your select business applications directly within Gmail. This feature was made available earlier this year as a developer preview but is now available to everyone from the gear icon in Gmail.
From our very good friends over at xda-developers.com