What a delightful thing Clive Thompson (one of Boing Boing's regular contributors) has created! It's called Weird Old Books, and it is a search engine that returns one pre-1927 book based on your search term.
He wrote about it on Medium:
— Read the restWhen I first starting crafting this, I had two design specs:
1) Immediate access
I wanted a tool that would only find you books in the public domain.