Convert from Hex to ASCII and back. Each line that is input will be processed individually. You may input Hex using the colon or hyphen character as the separator, or leave it out, and they will be grouped 2 characters at a time. Shift-enter, control-enter (if your browser supports it), or moving focus cause the form to change.
It's implemented in JavaScript with the help of the JQuery library. Thanks also to the creator of the Hex/ASCII Converter for ideas.