There are a few different types of add ons that can be used with Wrike. The first type is called a "Gadget" and these are little tools that can be used to add functionality to your Wrike account. For example, there is a Gadget that allows you to see a calendar view of your tasks, or one that allows you to create a to-do list.
The second type of add on is called an "Integration." Integrations allow you to connect Wrike with other apps and services that you use. For example, you can integrate Wrike with Google Drive, so that any attachments you add to Wrike tasks are automatically saved to Drive. Or you can integrate Wrike with Slack, so that you can get notifications about Wrike tasks in Slack.
Finally, there are "Premium Add-Ons." These are add ons that are developed by Wrike and are available for an additional fee. Premium Add-Ons add additional features and functionality to Wrike, such as the ability to create Gantt charts or to use Wrike's API.