There's plenty of software around for client machines that allow POP, IMAP, SMTP etc to be used for multiple accounts. It's a great way to keep all your email accounts managed in one location.

But is there any software on the web which does the same thing? Something like gmail, or what ever that connects to all your accounts, and has all your emails in the one place (Even though it's different accounts). Something like outlook, or Thunderbird.