Extensions are installable packages which give CiviCRM new functionality, and this directory provides a centralized list of extensions which the CiviCRM community has created.
This listing displays CiviCRM extensions that work on all Content Management Systems (CMS). You can also browse directories of plugins or modules that are made specifically for Backdrop, Drupal, Joomla and WordPress. There are also many more extensions in various stages of development available on CiviCRM's Gitlab.
Use this, if you have a lot of activities, and you're having troubles with the performance of the activity tab in the contact summary view, or the activity reports.