Google is making it possible for developers to bring their services into Gmail using new integrations called Add-ons. From a report on PCWorld: It's built so that developers can write one set of code in Google's Apps Script language and have their integration run in Gmail on the web, as well as inside Google's Android and iOS apps for the service. For example, a QuickBooks add-on would let users easily send invoices to people who they're emailing. Google already offers Add-ons for its Docs word processing and Sheets spreadsheet software. This sort of system could be useful for users because it helps them get work done without leaving Gmail. It also helps draw users into Google's official email app, rather than use one of the many other clients that can access the service, including Microsoft Outlook.