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Google Apps is a service from Google for using custom domain names with several Google products. It features several Web applications with similar functionality to traditional office suites, including: Gmail, Google Calendar, Talk, Docs and Sites.
The Standard Edition is free and offers the same amount of storage as regular Gmail accounts. The Premier Edition, which offers 25 GB of e-mail storage, is 50 USD, 40 EUR, or 33 GBP, per year, per account. The Education Edition, which is free, combines features from the Standard and Premier editions.
- February 2006
- Google created Gmail For Your Domain with an invitation-only beta, which allowed Gmail to be used with a custom domain name. It featured 2GB of e-mail storage, and many of the standard Gmail features.
- August 2006
- Google expanded on this service and developed Google Apps For Your Domain, incorporating more recent Google services, including Google Calendar, Google Talk, and Google Page Creator. Later, Google added a "Start Page" to all accounts, which is based on their iGoogle service.
- October 2006
- Google allowed educational institutions to sign-up for the service as well, which was retitled Google Apps For Education. A large implementation of Google Apps is at Lakehead University in Ontario, Canada, where 38,000 users have Gmail and in-browser IM capabilities.
- February 22, 2007
- Google launched a Premier Edition for enterprise, as well as making registration public for all Google Apps services. At the same time, all products were unified, and the online control panel was redesigned.
- June 2007
- Email migration from IMAP email services was added to Google Apps.
- October 3, 2007
- Google announced that "security, compliance, policy management, and message recovery services" from recently-acquired Postini will be integrated into Google Apps Premier Edition.
- October 12, 2007
- Google announced that e-mail storage for domains using Google Apps would be increasing. Premier Edition accounts now have 25GB of space each (previously 10GB). Standard and Education Edition accounts will mirror the Gmail counter (previously 2GB, over 7GB as of August 2008).
- February 28, 2008
- Google announced that Google Sites will be available to domains hosted by Google Apps. Google Sites allows collaborative editing of web sites and permits users to upload images and videos to their site.
- September 2008
- Google Page Creator and file uploader was removed as an available service for new Google Apps applicants.
- December 1, 2008
- Google removed the Start Page option for new Google Apps accounts. They are apparently trying to transition new users to using sites instead.
- January 14, 2009
- Google removed the ability to add additional users to Standard Edition domains and limited new standard edition domains to 50 users (a reduction from the previous 100).
- January 29 2009
- Google added Google Apps to the Google Labs suite. This allows users to add gadgets to their inbox such as 'Offline', 'Tasks', and 'Vacation Time!'.
- April 1 2009
- Google added theme support to the mail interface.
- July 7 2009
- Google upgraded all of the services under Google Apps from 'Beta' status.
- Sept 15, 2009
- Google announced that it will provide GovCloud, which will host Google Apps in a separate data environment with enhanced encryption for meeting state and government security standards. 
Differences between editions
Each edition has a limit on the number of users that may be active at any given time. Google Apps launched with a default user allotment of 200 users, which was shortly changed to 100 users. In addition, users could request to have their user limit increased through a manual process taking (at least) 1-2 weeks for approval. In January of 2009, the cap was changed so that all new accounts would receive only 50 users as opposed to 100, and could not request more without payment.  This was confirmed as relating to the launch of the Google Apps commercial reseller program. Existing Standard Edition users before January 2009 kept their old allocation, in addition to the ability their "request" more users, though these limit requests are now commonly answered with suggestions to "upgrade your subscription". 
The subscription level of a Google Apps edition is billed based on the total number of available users in the Apps account, and the edition features apply to all users accounts in that subscription. It is not possible to purchase upgrades for a subset of users: to increase the user limit, subscriptions must be purchased for all accounts. For example, an upgrade from a "Standard" limit of 50 users to allow up to 60 users would involve paying for 60 users, whether they are used or not.
Differences between editions:
- Standard Edition
- Same storage space as regular gmail.com accounts (over 7.4GB as of December 2009)
- Text ads mandatory
- Limited to 50 Users
- Email attachments cannot be larger than 25 megabytes.
- Limited to sending email to 500 external recipients per day per email account.
- Premier Edition
- 50 $USD / account / year
- 25 GB space for e-mail
- Text ads optional
- Integrated Postini "security, compliance, policy management, and message recovery services"
- Conference room/resource scheduling
- 99.9% e-mail uptime guarantee
- APIs for Single Sign On, etc.
- 24/7 phone support
- 3rd party applications and services
- Google Video (Private company version of Youtube.)
- Limited to sending email to 2000 external recipients per day per email account.
- Education Edition, same as Premier Edition except for:
- Free for "accredited not-for-profit K-12 schools, colleges, and universities"
- No ads for faculty, staff, or students
- Google may serve ads to accounts not associated with enrolled students, non-profit staff or volunteers 
- Limited to 30000 Users
- Same storage space as regular gmail.com accounts (over 7GB as of June 2009) 
- Beswick, James (2009). Getting Productive With Google Apps. San Francisco, CA: 415 Systems. ISBN 9781440486760.
- Conner, Nancy (2008). Google Apps: The Missing Manual. Sebastopol: Pogue Press. ISBN 9780596515799.
- Granneman, Scott (2008). Google Apps Deciphered: Compute in the Cloud to Streamline Your Desktop. USA: Prentice Hall. ISBN 9780137004706.