Chrome extensions have a more global effect on the browser. For instance, a Chrome extension might let you take a screenshot of an entire website and save it to an image file. After installing the extension, you'll have access to it on any website you visit because it's installed to the whole browser.
Unlike Chrome apps, extensions are actually small programs that download to your computer in the form of a CRX file. They're saved to a specific location within Chrome's installation folder, so you can't typically choose where on your computer to save the extension. Chrome stores it somewhere safe and can use it anytime you open the browser.
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Add-ons run inside Google Sheets, Docs, Slides, and Forms. (Source)
- Push to Classroom: Push to Classroom allows teachers to instantly share any link to their Google Classroom classes as an announcement or an assignment. This allows teachers to instantly push links to their students, even if the students aren't currently logged in to Google Chrome.
- Formenate: Converts items in a numbered list to questions on a Google Form or quiz. A quick and simple way to get your questions and answers from Google Docs to a Google Form. This add-on uses the numbered list in a Doc to generate the questions and answers in a Form. To use, format your text using a numbered list with the questions having a number and the answers having a lower case letter. Start Formenate and choose the options you want in the sidebar. When you click on the Formenate button, the Google Form is generated. A link to edit the Form further and a link to preview the Form will be added below the Formenate button. For more information, see this article.