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:

Omnipay is an open source payment processor library that supports multiple payment processors (around 30 currently). https://github.com/omnipay/omnipay...
Current Usage: 211
The Advanced Fundraising extension provides a series of reports to help fundraisers view their progress in greater detail....
Current Usage: 211
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: 208
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: 208
You like how tags are displayed in the contact summary? this extension does the same, for groups. You can also add the contact to a group from the summary (click on the Groups label)...
Current Usage: 204
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: 202
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
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
Automatically corrects email addresses when they're added, and allows for mass correction. Rules can be configured.
Current Usage: 103
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
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