This is a great project by Tim Devin, a Boston-based conceptual artist and writer.
From the website:
About this magazine
Each month or so, we release a new issue of "i left this here for you to read." We then leave them in public places (such on park benches, on buses, in airports and dentists' offices...) for anyone to take--free of charge.
Currently, we distribute our magazine in Boston, New York, and LA. We only print about 50 copies of each issue, and don't reprint any past issues. Sorry, we can't mail you any copies--we only send them to contributors.
Email us at firstname.lastname@example.org
They accept submissions of writing, art, and even objects. And they automatically include every single thing they receive. Of course I sent them something! Go here for more info.