Extensions are installable packages which give CiviCRM new functionality, and this directory provides a centralized list of extensions which the CiviCRM community has created.

Further resources:

Multisite (url) based permissioning.   This is a port of the drupal multisite module to an extension. It allows the CiviCRM multisite concept to be extended such that the site a contact logs onto will affect which contacts they can see and edit....
Current Usage: 109
Implements hook_username_alter() so that, if available and non-empty, the CiviCRM "Display name" is shown in place of the Drupal login name for username displays....
Current Usage: 107
What is CiviBooking? Are you a non profit with Rooms or Resources that you think you could raise money by renting out? Or are you a community center or voluntary service looking to manage your resources better? Sick of spreadsheets, emails and that Google calendar that no one keeps up to date? Then CiviBooking is the extension for you!...
Current Usage: 95
This extension improves the default search in several ways: more efficient requests search in the start of the names instead of in the middle (first or last) adjust based on the length of the query and the number of results to do the query(ies) that are the most efficient Give it a go and let me know what you think of the result....
Current Usage: 92
A tool that allows you to easily correct invalid phone numbers.
Current Usage: 89
Creates Tax Receipts including single or annual/aggregate tax receipts, with distribution by email or print, detailed reporting, press ready PDF template possible. We worked with (and continue to work with) a BDO Tax Partner who has strong ties to both the NPO community and Tax Authorities (CRA)....
Current Usage: 86
This is a civicrm extension to export directly into an excel format instead of the default csv. If you never had any problem with opening a csv into excel, this extension won't help you (and you are likely to be a US user dealing with english names)...
Current Usage: 85
If you are in Europe and use CiviCRM to manage recurring contributions, you need this extension. Warning: upgrading to 1.2.4: If you're using the payment processors, please verify and re-save your payment processor settings! If you've been using the SEPA tokens, you'll have to adjust your templates SEPA Direct Debit Module...
Current Usage: 85
From 22 April 2013, UK based charities and Community Amateur Sports Clubs can sign up to make repayment claims electronically. The new service, Charities Online, is being introduced in response to customer feedback. It will make repayment claims faster and easier by filing online. The current R68(i) print and post repayment form will be replaced by three options for making claims....
Current Usage: 77
CiviRelate creates a CiviCRM relationship between the acting user and a CiviCRM contact created by the acting user through the submission of a designated CiviCRM profile form. CiviRelate has a simple configuration page to define the Profile to use and the relationship to create....
Current Usage: 73
This extension has been incorporated into core as of CiviCRM 4.6, so the 4.5 version will not be updated....
Current Usage: 72
“Simple Donate” extension which allows the administrator to link existing donation pages with our new sleek, user friendly and responsive donation page....
Current Usage: 72
Introduction The Capitalisation Corrector is a CiviCRM extension that creates a scheduled job that corrects the capitalisation of contact's first and last name. Only contacts of the type 'Individual' are corrected and only names that are in all lowercase or all uppercase will be corrected....
Current Usage: 70
Sunlight Congressional Districts - Fetches data about the current members of Congress using the Sunlight Congress API.http://services.sunlightlabs.com/docs/Sunlight_Congress_API/...
Current Usage: 70
This extension changes the default so it doesn't send a confirmation email when registering a contact to an event from the back office. Nothing more,  really simple but avoids sending emails by mistake....
Current Usage: 70