As you might guess, nearly all of what I found in the collections on The Public Domain Review is content of a historical nature. The collections include short descriptions that explain the significance of the media you're accessing.
Applications for Education
The Public Domain Review could be a great place to find historical media to use in history lessons, literature lessons, and art history lessons. If you're looking for colorful imagery to use as filler or backgrounds in slide presentations, the collections on The Public Domain Review are probably not your best bet. In that case, I would look to Pixabay for images that are in the public domain.