Which of the following applications does not have add-ons available?

Google Keep is designed primarily as a note-taking service and does not support the add-on functionality that other Google Workspace applications like Docs, Sheets, and Forms do. The purpose of add-ons is to extend the capabilities of tools by allowing third-party applications to integrate additional features directly within the Google environment. For instance, in Docs, users can enhance their writing experience with various tools; in Sheets, data analysis and visualization can be improved through add-ons; and in Forms, new functionalities can augment the survey and form creation process. Keep, however, focuses on simplicity and ease of use for capturing and organizing notes, making it inherently different in functionality and purpose from the other applications.