I could see it being used for screenshots of text to draw attention to certain points. Tweets, facebook posts, etc.

Code-annotated screenshots would be rad, a bit like LogRocket logs a session, but static, so you can receive feedback and immediately act on it.

Killer features also as GitHub Action/App

Generate a shareable/anotable link on every branch/pr

Make annotations back to GitHub issues, so they can be tracked/resolved there, and added back to the annotation UI as such.

And I could keep going...

For your personal note taker for content based sites like NYTimes. It can store them in localstore or on the cloud.