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: 641
This extension adds the possibility to export directly into the MS Excel (.xlsx) format, instead of CSV (less fiddling, easier to use). It supports exporting from reports and from search results....
Current Usage: 634
This extension provides additional mail merge tokens for CiviCRM for use in emails, mass emails, or PDF letters....
Current Usage: 602
Extension to support General Data Protection Regulation
Current Usage: 578
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: 561
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: 546
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: 545
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: 519
E-mail API for CiviCRM to send e-mails through the API
Current Usage: 511
Allows Drupal's cron to invoke CiviCRM's cron.
Current Usage: 509
Tokens for CiviCRM including formatted address block (with country formatting), today's date, userID, phone, membership & relationship token
Current Usage: 501
Provides integration with Clickatell SMS gateway for sending single and mass messages.
Current Usage: 472
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: 459
Event Calendar Extension allows you to view all CiviCRM events in a calendar by month,day,week. The setting page allows us to select which events should be shown on calendar with the color we want for particular event type. Also the title for Event Calendar. Below is the Screenshot of Setting Page of Event Calendar ...
Current Usage: 343
Normalise the data entered in several fields. So far firstname, last name... so they are Properly Capitalised What does it do? It modifies profiles and the normal contact edit/add so when you type (or paste) XAV as the first name, it converts it into Xav...
Current Usage: 331