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:

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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Geocoder extension provides geocoding from multiple providers (default is Open Street Maps) with advanced features over core geocoding Requires - CiviCRM 5.x, php 5.6 Credit : the Wikimedia Foundation
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CallHub is a hosted phone banking service that enables your staff to talk with your contacts over the phone banking campaign and store notes about the call....
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This is a CiviCRM extension designed for large scale donation receipt generation in a heavily regulated environment (e.g Germany).
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This extension has been developed for the test purpose only....
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Places recently-viewed items in the Menu bar for quick access.
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SparkPost / CiviCRM Integration Integrates SparkPost to CiviCRM, so email can be sent out over the SparkPost service and bounces can be processed in CiviCRM. * Now processes bounces for Transactional and Bulk (CiviMail) emails....
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Supports easy creation of outbound email messages in Outlook or similar email reader.
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View and respond to inbound SMS messages. To view, click on Mailings then SMS Inbox.
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CiviCRM-Secure-Trading-Payment-Processor for CiviCRM 4.3...
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