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:

The Campaign Manager takes working with CiviCRM's campaigns to the next level. You'll love the new stats,KPIs, and hierarchies of campaigns.
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This is a simple CiviCRM report giving you a list of the upcoming birthdays of your contacts. Simply install the extension, create a new report, and use "Available for Dashboard" to give you the list upon login....
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http://drupal.org/sandbox/leez/1929728 A drupal module for querying a CiviCRM database for donor patterns (overview, new, lapsed, upgraded, downgraded, maintained) and producing CSV files from the results....
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Manual Direct Debit
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This extension provides fieldset on new contact form for adding relationship(s).
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This CiviCRM extension adds some contribution related functionality that I find useful for our CiviCRM instance....
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When CiviCRM geocodes an address, the geocoding service generally returns much more information than CiviCRM uses. This extension allows site administrators to set a policy for what to do with that information on a field-by-field basis: discard it, fill in missing data, or overwrite existing data....
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The CiviMobileAPI extension (com.agiliway.civimobileapi) is a CiviCRM component that allows to use a mobile application CiviMobile.
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Integrates CiviCRM with Sharepoint
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Extended membership report with support of filtering/showing custom fields of Individual contact.
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This extension adds a new API to CiviCRM: Entity is FinancialItem, action is Get. You can also use the derived actions getsingle, getvalue, getcount etc....
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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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This extension makes the checksum of the contact available for exporting.
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Provides functions to look up address meta-data from Postcodes.io: admin district, geolocation, and county.
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GoCardless Payment Processor for CiviCRM...
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