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:

This is an integration module for sites running CiviCRM and the Domain Access module.  By default, when creating a user in Drupal, Domain Access will automatically assign the user to the domain on which they registered.  However, if they create their user via a CiviCRM profile, they will not be added to the appropriate domain.  This module fixes that....
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CiviCRM native extension to check if the CMS is in maintenance mode when I get a REST API and return error if so.
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This extension helps you creating custom API's that retrieve query result data. If an external application needs information from CiviCRM that cannot be expressed using API parameters, you can use this extension. It allows you to create a custom API that returns data from an SQL query, in a way that you can use API filters, options and joining as always....
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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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This module offers a fully configurable/extendable Drupal view that provides the functionality to search from a postcode and a distance.
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Adds tokens for use in emails and mail merges. Tokens include client name(s), plus the name, email, phone and address of all case roles....
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This ia a CiviCRM extension that adds much needed flexibility to scheduled jobs. It accomplishes this goal in two ways......
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Send email notification to event speakers when a new individual registers....
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Adds over 20 new fields to Summary Fields, including contributions by related contacts, plus fields for CiviMail, CiviEvent, and CiviGrant.
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CiviCRM Extension for CiviCRM Contribution and Contact synchronization with QuickBooks Online, http://www.intuit.com.au
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