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:

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: 444
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: 418
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: 405
CiviCRM GiftAid Extension
Current Usage: 350
Tokens for emails: Supports events, contribtion pages, profiles, forms, petitions, addressing couples, nicknames. Links include checksum.
Current Usage: 346
This extensions makes the permission flag on a contact's relationship work as a true ACL.
Current Usage: 344
This extension adds a block to the contact summary that allows editing of any configured relationship type with a UI similar to the employer field.
Current Usage: 342
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
Current Usage: 336
This extension allows users to get their CiviCRM assigned activities into their Google Calendar or similar calendaring applications, by providing a feed of each user's assigned activities in iCalendar format, ready to be subscribed to from within Google Calendar, Outlook, etc....
Current Usage: 309
You like how tags are displayed in the contact summary? this extension does the same, for groups. You can also add the contact to a group from the summary (click on the Groups label)...
Current Usage: 304
Provides integration with Clickatell SMS gateway for sending single and mass messages.
Current Usage: 300
This CiviCRM extension normalizes your data before it is saved to the database. It therefore works from the back-end, with public form submissions such as profiles, contribution, event registration and membership creation/renewal pages as well as with data imports. It can normalize first, middle, last and company names, phone numbers, and addresses including zip codes....
Current Usage: 298
Omnipay is an open source payment processor library that supports multiple payment processors (around 30 currently). https://github.com/omnipay/omnipay...
Current Usage: 293
Sagepay using the Omnipay multiprocessor extension.
Current Usage: 293
Helper extension to manage settings for multiple entities This extension does not do anything on it's own. Rather it supports other extensions by storing settings related to entities without the requirement to create a table per extension....
Current Usage: 276