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: 443
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
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: 384
CiviCRM GiftAid Extension
Current Usage: 382
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: 375
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: 373
Tokens for emails: Supports events, contribtion pages, profiles, forms, petitions, addressing couples, nicknames. Links include checksum.
Current Usage: 372
This extensions makes the permission flag on a contact's relationship work as a true ACL.
Current Usage: 345
This extension allows a staff user to add, edit and delete line items of a contribution.
Current Usage: 330
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: 315
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: 306
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: 302
Provides integration with Clickatell SMS gateway for sending single and mass messages.
Current Usage: 281
Omnipay is an open source payment processor library that supports multiple payment processors (around 30 currently). https://github.com/omnipay/omnipay...
Current Usage: 278
Sagepay using the Omnipay multiprocessor extension.
Current Usage: 278