Anki's capabilities can be extended with add-ons. Add-ons can provide features like extra support for specific languages, extra control over scheduling, and so on.
To browse the list of available add-ons, select the Tools>Add-ons menu item, then click on Get Add-ons.
If you have downloaded an add-on that is not working properly, or if you accidentally made a mistake when editing an add-on, you can use the "Delete" option in the menu to remove it.
Add-ons use and modify arbitrary parts of Anki’s codebase, so in some cases, updating Anki can break the compatibility with older add-ons. If one of your add-ons stops working after updating Anki, please consider reporting the issue to the add-on author. If you rely on this add-on, you will need to keep using an older Anki version until the add-on gets an update.
There is a "Contact Author" button on most add-ons pages on Ankiweb, and many authors include their email address in the add-on, so if you need to get in touch with the author, editing the add-on and looking at the top of the file may help.
To learn how to write your own add-ons, please see the add-on writing guide.