StackMail is an email-based web service for the StackExchange sites. The concept is simple: send an email to
firstname.lastname@example.org with one of the commands as the subject line - and presto! You will receive a reply with the results.
If you just want a demonstration, (and I'm sure you do) send the following as the subject line:
...and you will receive a reply with the list of commands and what they do. Some more ideas:
stats meta user 18 stackapps questions serverfault
Eventually, as more methods are added, you will be able to search for questions, users, etc.
Any email client that can send and receive text-based email.
I can be reached at email@example.com
Yet another application that uses my stack.PHP wrapper.