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:

Provides tools for signing up, managing and tracking volunteers
Current Usage: 684
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: 664
This extension provides additional mail merge tokens for CiviCRM for use in emails, mass emails, or PDF letters....
Current Usage: 586
Extension to support General Data Protection Regulation
Current Usage: 584
Allows Drupal's cron to invoke CiviCRM's cron.
Current Usage: 553
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: 547
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: 536
E-mail API for CiviCRM to send e-mails through the API
Current Usage: 533
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: 532
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: 515
Tokens for CiviCRM including formatted address block (with country formatting), today's date, userID, phone, membership & relationship token
Current Usage: 514
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: 471
Provides integration with Clickatell SMS gateway for sending single and mass messages.
Current Usage: 448
A log viewer for the CiviCRM debug log, showing a summary with links to a detailed view of each log entry.
Current Usage: 369
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: 346