The Wayback Machine - https://web.archive.org/web/20160924013806/https://developers.google.com/google-apps/

Build on top of Google Apps

With Apps Script, you can build add-ons for Sheets, Docs, or Forms, automate workflows, and talk to other APIs.
Apps Script Add-ons

Back up your users' stuff

The Drive API lets you sync data from your app with your user's Google Drive account, so it's available everywhere.
Drive for Android Drive for iOS Drive for Web

Integrate with users' Google accounts

Our REST APIs let your app work with users' mail, calendars, contacts, and other data.
Calendar Contacts Tasks

Create interactive cards and buttons in Gmail

Emails with markup appear in Google Search results when users look for tickets, flights, and events. Your markup will also help Google Now bring users the right information at just the right time.
Email Markup Google Schemas Gmail API

More APIs for interacting with Google Apps

Apps Activity API

 Track changes to a user's Google Drive files, including new comments and other activity.

Calendar API

 Create new events in a user's Google Calendar, edit or delete existing events, and search for events.

Contacts API

 Work with a user's Google Contacts data to add new entries, edit or delete existing contacts, and query for particular criteria.

Drive API

 Interact with nearly any aspect of a user's Google Drive, including permissions, file revisions, and connected apps.

Gmail API

 Read messages from Gmail, send email, modify the labels applied to messages and thread, and search through existing mail.

Picker API

 Google Picker lets users select photos, videos, and documents stored in their Google account, then pass them to your app.

Realtime API

 Give your users the power of Google Docs-style realtime collaboration. All JavaScript. No server.

Sheets API

 Create and manage nearly every aspect of Google Sheets data, including the content, arrangement and appearance.

Sites API

 Create or copy Google Sites, work with pages, templates, and comments, upload and download attachments, and more!

Tasks API

 Manage a user's Google Tasks list, which can be seen in Gmail, Google Calendar, and elsewhere.

APIs and tools for domain admins

Google Apps Marketplace

 Enterprise applications that can be added to a Google Apps domain. Developers can publish apps to the marketplace for domain admins to discover and install.

Admin SDK

 A suite of tools and APIs to help admins migrate to Google Apps, create custom usage reports, and manage users, groups, and devices.

Admin Settings API

 Manage the settings for Google Apps domains, including most of the features offered in the Google Apps Admin console.

Calendar Resource API

 Work with Google Calendar resources other than users, like conference rooms, projectors, or company vehicles.

Directory API

 Our most popular admin API! Manage mobile and Chrome OS devices, groups, group aliases, members, organization units, users, and user aliases.

Domain Shared Contacts API

 Manage external contacts that are shared with all users in the domain. For internal contacts, use the Directory API instead.

Email Audit API

 Audit email, email drafts, and archived chats for users within the domain, retrieve account login information, and download users' mailboxes.

Email Settings API

 Manage user-level email account settings, including most of the options shown in a user's mail settings screen.

Enterprise License Manager API

 Assign, update, retrieve, and delete user licenses for Google Apps, including Google Apps Vault, Google Maps Coordinate, and extra Google Drive storage.

Groups Migration API

 Move emails from public folders and distribution lists for legacy email systems into Google Groups discussion archives.

Groups Settings API

 Manage settings for Google Groups, including notifications, archives, moderation, and access for internal and external users.

Reports API

 Create usage reports like sign-in frequency or user activities in specific Google Apps, like the admin console and Google Docs.

Reseller API

 For a domain managed by a Google Apps reseller, place orders for features or users and coordinate monthly post-pay subscriptions.