There are three editions of Google Apps, each addressed to institutions with different needs:

Google Apps Standard Edition. Is the version designed for small and medium enterprises without advanced integration needs with internal systems. No annual fee.

Google Apps Premier Edition. It is the advanced version of Google Apps. It is intended for businesses or corporations in need of integration with internal systems, policies to control e-mail (Postini), email archive and more storage. It has an annual cost per user.

Google Apps for Education. It is the version for educational institutions or nonprofits For no annual fee. Contains all functions of the Premier version, except for storage space.

Here you can review the service agreements for the various editions of Google Apps.

Comparative Table of Google Apps Editions

	Premier	Education	Standard
Maximum Account Number	Unlimited	Unlimited	50
E-Mail Storage per account	25Gb	7 Gb	7 Gb
Google Docs
Google Sites
Google Talk
Google Video
OpenID/Single Sign On
Programming API
Postini Message Security
Historic E-Mail Archiving (Extra charge)
E-Mail Migration Tool
Outlook Sync Plugin
99.9% SLA
Disclaimer: Google Video has 3GB of Storage for the Premier Edition and 10 GB for Education Google Sites has 10 GB of Storage + 500 MB per user account. Education Edition has 100GB Of Total Space. Standard Edition has 10 GB. Historic E-Mail Archiving has an extra cost. A substantial discount to educational institutions it is offered. Mail Migration for the Standard Edition is posible through other methods not provided by Google Directly.