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 Hebrew Calendar extension for CiviCRM has a variety of functionality,  including mail merge tokens for sending yahrzeit reminders, birthday wishes, Hebrew demographic information, Hebrew date of birth, next Hebrew birthday, yahrzeits, APIs and more....
Current Usage: 197
Extension to facilitate postcode lookup feature in CiviCRM using AFD, Civipostcode, Experian, PostcodeAnywhere or getaddress.io providers.
Current Usage: 195
ReportPlus extends the default CiviCRM Form's Framweork adding new features
Current Usage: 185
This CiviCRM extension provides a daily scheduled job named "Call Email2Each.Sendemails API (Daily)"  This job expects 2 parameters: a group name and a message template name.  When this job runs,  it will send an email to each contact in the group/smart group. The contents of the email will be the message template. ...
Current Usage: 173
Adds over 20 new fields to Summary Fields, including contributions by related contacts, plus fields for CiviMail, CiviEvent, and CiviGrant.
Current Usage: 171
A tool that allows you to easily correct invalid phone numbers.
Current Usage: 168
Allows adding an automatically calculated "Additional Percentage" field to any price set (e.g., add 3% to cover credit card fees).
Current Usage: 168
Keep track of which extensions override core files, and to detect when a core file that's been overridden gets updated
Current Usage: 165
When viewing Contact Summary page Contributions tab, displays the balance due for each row on the list of contribution.
Current Usage: 164
PDF API for CiviCRM to create a PDF file and send it to a specified e-mail address. This is usefull for automatic generation of letters The entity for the PDF API is Pdf and the action is Create. Parameters for the api are specified below:...
Current Usage: 160
Adds bounce handling, and mailing reports for CiviCRM's transactional emails and creates Activities for mail such as Receipts and Invoices.
Current Usage: 154
Membership Extras for CiviCRM
Current Usage: 151
Onscreen tutorials for learning to use CiviCRM
Current Usage: 150
Store documents on the contact dashboard A document can be linked to more than one contact Version management with a document Custom search to find documents  ...
Current Usage: 146
Multisite (url) based permissioning.   This is a port of the drupal multisite module to an extension. It allows the CiviCRM multisite concept to be extended such that the site a contact logs onto will affect which contacts they can see and edit....
Current Usage: 146