Tell me about Google add-ons!

In the past year, I've learned about several useful Google add-ons: Doctopus, Goobric, Easy Accents, Speech Recognition, Extensis Fonts, and WeVideo. All of them are free, and they were all very easy and quick to install. 

Doctopus and Goobric work together to allow teachers to attach rubrics to students' writing in Google Classroom and to score them online. Students immediately have access to the rubrics and their teachers' comments. 

Easy Accents, once installed, allows users to display a side menu of letters with accent marks for users writing in Spanish or other languages that utilize accent marks. This is so much easier for students than having to click 'insert' and then 'symbol' or to push the 'alt' key along with a numeric code. 

Speech Recognition allows users to dictate into a microphone, built-in or connected to their computer, resulting in text. This has empowered students who have valuable ideas to express, but struggle with writing. 

Extensis fonts installs thousands of fonts that Google Docs users can choose from, and WeVideo is a recording and editing program that allows users to quickly, easily export their recordings to Google Drive or other destinations. 

Discovering these free, useful add-ons has created one huge question in my mind: What else is there?! I can't believe I didn't know about these add-ons for so long, I can't believe they're free, and I wonder what other useful add-ons exist that may be useful to me, my students, and my fellow teachers. I'm on a quest! 

Please share any useful Google add-ons you have discovered and how you use them, especially if they're useful in K-12 education.