Inspired by Adam Kalsey's SimpleTrack, I wrote my own PHP script called Manual Trackback. (To be honest, I was chicken to ask Mr. Kalsey for a copy of his script.) This script allows an author of a weblog that does not support trackback to manually trackback to my weblog. All this weblog author needs to supply is the title of his or her weblog, the title or date of his or her weblog entry, the entry's URL, and an excerpt. That's it.
The Manual Trackback script is completely customizable to your weblog if you know a little HTML and CSS. There is also a minimum of error checking. It should work for other weblog systems besides Movable Type as long as they stick with the trackback specifications.
There is one PHP include required for this script to run. It is an open-source PHP class called Snoopy. You can download a copy of Snoopy from SourceForge.net. (Thanks to Mr. Kalsey for the hint.)
The Manual Trackback script can be launched from a GET URL or from a POST form with your trackback URL, and optional entry title and its URL, from anywhere with in your weblog. (The individual entry archive page or main index page seem like the most logical places.)
Documentation is included within the Manual Trackback script.