Web2Tor and Tor2Web are reverse proxies which allows clearnet users to access Tor Onion Sites (AKA Hidden Services), and there are a variety of services available online (such as onion.to, onion.cab, onion.city and onion direct) running this service.
This post details why using these is such a bad idea, as well as detailing some of the changes I'm making to the site to help discourage use of these services.