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:

CiviCRM-Secure-Trading-Payment-Processor for CiviCRM 4.3...
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This very tiny extension enables validating a checksum (combination of contact_id and checksum) with an API.
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When a home address for an Individual contact in Austin, Texas is added to CiviCRM when importing or manually this extension finds its City Council District using shape files produced by the City of Austin Texas and GEOS - Geometry Engine, Open Source and sa...
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PayZang has developed a payment processor plugin for CiviCRM (4.2.9) on Drupal that allows organizations to accept ACH and Credit/Debit Card payments. This plugin allows you to do recurring as well one-time payments using both ACH and Credit/Debit Cards....
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This extension exposes table name/column name/machine name fields to the custom data UI.
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DONOR MANAGEMENT SOLUTIONS + PAYMENT PROCESSING PTC offers innovative solutions such as mobile giving, event registration and donor management combined with cost-effective, secure payment processing that is easy to integrate with your current Civi database and website. Reach donors in new ways and raise more funds for your church or non-profit organization....
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Starting with CiviCRM 4.7, the system check mechanism allows extensions to define new checks and the status messages to appear on the system status page.  This extension has two purposes...
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The form processor extension gives you the ability to define business logic for handling form submissions (from external websites).
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Extended Contact Summary report with support of filtering/showing custom fields of Individual contact along with Membership Type.
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This extension adds functionality to add attachments to message templates. You can add attachments to templates by editing the message templates under Administer --> Communication --> Message templates. Updating a template through the e-mail screen does not work....
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CiviCRM Extension for CiviCRM Contribution and Contact synchronization with QuickBooks Online, http://www.intuit.com.au
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Allows adding an automatically calculated "Additional Percentage" field to any price set (e.g., add 3% to cover credit card fees).
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This is a fairly simple extension that adds the field "duration" to the email "action" form sent at the contact level. Some clients need to record their time (in mins) for each activity they do, whether that activity is a "meeting", "phone call" or "email", their time is required to be recorded and made available within the activity report....
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You can use this CiviCRM extension if you want to create a settings form for your own extension.
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CiviCRM extension to link CiviCRM to the 'Kadervormingstool' of the Flemish government. Work in progress. See the github project page for more info: https://github.com/Chirojeugd-Vlaanderen/kavo...
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