Mail to Web
This is usually done by editing the mailserver alias file to route an address to a script, however on shared hosting this isn't always possible (probably closer to this is hardly ever possible). Generally in your shared hosting administration, you don't see that kind of option. And they don't usually let you edit the mail alias files yourself.
But just give your script URL to mailhook, and you get a hostname to send messages to. Any e-mail sent to that hostname (or any domain that has that host as a MX record) gets sent to your script with a simple HTTP POST (the same method used by web forms).
Very nice concept. Too bad it doesn't seem to be working now.
If you're writing something like a listserver, something tells me you better just process the mail yourself. But if you just want to be able to e-mail your blog, or add e-mail functionality to a site on shared hosting, this could be very useful.