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:

The Advanced Fundraising extension provides a series of reports to help fundraisers view their progress in greater detail....
Current Usage: 238
This extension is designed to preserve the email reputation of your server and its IP by ensuring that all outbound email is sent from an address with the same domain as the System-generated Mail Settings From Email Address configured at Administer > Communications > Organization Address and Contact Info (civicrm/admin/domain?action=update&reset=1)....
Current Usage: 238
Extension to facilitate postcode lookup feature in CiviCRM using AFD, Civipostcode, Experian, PostcodeAnywhere or getaddress.io providers.
Current Usage: 235
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: 227
This extension loads United States counties when you first install it.  Once enabled, it does nothing.  You may disable it or uninstall it, and nothing will happen: the counties will remain loaded in your database.  If you re-enable it, it will check for missing counties and just add those....
Current Usage: 223
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: 211
This Hebrew Calendar extension for CiviCRM has a variety of functionality,  including mail merge tokens for sending yahrzeit reminders, birthday wishes, Hebrew demographic information, Hebrew date of birth, next Hebrew birthday, yahrzeits, APIs and more....
Current Usage: 207
Omnipay is an open source payment processor library that supports multiple payment processors (around 30 currently). https://github.com/omnipay/omnipay...
Current Usage: 206
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: 195
This extension adds a pivot report that suppots multiple CiviCRM entities.
Current Usage: 195
Displays CiviCRM events in a calendar using the "fullcalendar" jQuery plugin.
Current Usage: 186
Core searches on telephones and emails search only for the Primary telephone and Primary email. This extension provides a custom search that looks for primary and non-primary telephone and emails that match the criteria, and displays all of the phone numbers and emails for those contacts....
Current Usage: 133
The CiviCalendar extension is an CiviCRM component which allows visualizing different types of cases, events and activities.
Current Usage: 125
The Database Health Report  provides you with a snapshot of your CiviCRM database's usage. It reports the last login time and number of contacts and activities modified by each user. WIth this report, you can evaluate the effectiveness of staff trainings, or get a quick glimpse into which users are active and who may need more prodding....
Current Usage: 116
Automatically corrects email addresses when they're added, and allows for mass correction. Rules can be configured.
Current Usage: 103