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:

Over-riding tpls is awful & hard to sustain. But if you HAVE to do it this extension could help. By default CiviCRM allows you to override the tpl for a given contribution page by putting the file in the path yourcustomtemplatefolder/CRM/Contribute/Form/Contribution/   If you want to override ONLY contribution page 6 then...
Current Usage: 38
This extension suppresses name and address fields from the billing block if they are in a profile and uses the profile fields instead. It prefers address fields that are more likely to be billing fields....
Current Usage: 37
Tokens for CiviCRM including formatted address block (with country formatting), today's date, userID, phone, membership & relationship tokens
Current Usage: 37
Extension deals with situation where sites have many short-term contribution pages that may later be disabled. Sometimes these pages are google indexed and people go to them wanting to donate....
Current Usage: 37
More info to come - but this extension provides custom searches written for the Australian Green Party by Andrew McNaughton to help manage Australian contact data by finding spam users and addresses in need of some manual checking....
Current Usage: 36
CiviHR is an integrated Human Resource Management application designed to meet the needs of non-profit and third sector organizations. CiviHR will be developed in multiple phases. Current version of CiviHR includes the following functionality:...
Current Usage: 35
Drupal project page: http://drupal.org/project/civicrm_private_report...
Current Usage: 34
This module makes it easier to configure settings in CiviCRM by:...
Current Usage: 32
This module makes it easier to configure settings in CiviCRM by  ...
Current Usage: 32
This extension makes it easy to have all email sent from Outlook stored on the appropriate contacts' records as Email Activities in CiviCRM. Code in Outlook talks directly to CiviCRM native APIs. The next version of the integration (hopefully out early fall 2015) will integrate Outlook Calendar with CiviCRM....
Current Usage: 32
This CiviCRM extension provides two way synchronisation between CiviCRM groups and MailChimp Lists. Changes to users in regular groups are synced with MailChimp in real-time, smart groups use CiviCRM's Scheduled Jobs to sync up. Changes made on MailChimp are sync'd back to CiviCRM using Webhooks...
Current Usage: 29
SYSTOPIA OpenStreetMap CiviCRM Geocoder This CiviCRM extension adds the Nominatim OpenStreetMap server as a geocoding option. Just install the extension, and activate via "Administer" => "System Settings" => "Mapping and Geocoding"....
Current Usage: 28
This CiviCRM extension allows you to limit the display of individual prices in price sets to specific groups. This allows you to implement things like members-only pricing for events. (by using a Smart Group to track current members) This extension works with both static and smart groups....
Current Usage: 27
Omnipay is an open source payment processor library that supports multiple payment processors (around 30 currently). https://github.com/omnipay/omnipay...
Current Usage: 27
Komfortables Erstellen von Einzel- und Sammelbescheinigungen für steuerlich absetzbare Zuwendungen. Weitere Informationen zu Einsatzgebiet, Funktionsweise, Bedienung und Entwicklungsstand finden sich auf unserer offiziellen Webpage der Spendenbescheinigungs-Extension....
Current Usage: 27