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 a payment processor extension for the iATS Payments payment processing service, making use of the web services interface.
Current Usage: 852
Exports reports and search results directly into the native MS Excel format (xlsx).
Current Usage: 813
Provides a way to keep Mailchimp Lists and CiviCRM groups in sync.
Current Usage: 755
Extension to support General Data Protection Regulation
Current Usage: 749
E-mail API for CiviCRM to send e-mails through the API
Current Usage: 710
Provides tools for signing up, managing and tracking volunteers
Current Usage: 701
Once installed, an 'API Key' tab will be available on contact screens for which you are authorized to manage the API key for this contact. You are authorized either if the contact if yourself, or if you are an administrator with the 'edit all contacts' permission....
Current Usage: 617
Twilio and CiviCRM integration allows delivering single and mass short message service (SMS) messages through its Twilio Gateway to mobile phone users. Download Link: https://github.com/civicrm/org.civicrm.sms.twilio/releases/latest...
Current Usage: 567
Tokens for CiviCRM including formatted address block (with country formatting), today's date, userID, phone, membership & relationship token
Current Usage: 558
Allows Drupal's cron to invoke CiviCRM's cron.
Current Usage: 547
This extension provides additional mail merge tokens for CiviCRM for use in emails, mass emails, or PDF letters....
Current Usage: 538
This extension allows CiviCRM to send emails and process bounces through the SparkPost service. It was designed with the following goals and/or features:...
Current Usage: 537
Mobile application for few specific actions in CiviCRM Current feature includes: * Contacts - Search Contacts - Add/Update/View Contacts - Proximity search for contacts * Events - participant search and checkin * Survey - Search for suvery - Record survey responses    ...
Current Usage: 527
A log viewer for the CiviCRM debug log, showing a summary with links to a detailed view of each log entry.
Current Usage: 523
Sometimes CiviCRM can be real tough to debug. Especially when you are getting fatal errors, but only by some users, and you can't recreate the problems. This utility will send you a detailed email when a CiviCRM fatal error occurs.
Current Usage: 519