Ph servers exist at many colleges, universities, and academically-affiliated research institutions throughout the U.S. and elsewhere. Mac Ph allows you to query these servers for address and/or e-mail information for faculty/staff/students at those institutions. (Thanks to Andrew Starr for this excellent description.)
Can't find what you're looking for? Try a search:
Also, if you have an older Mac, be sure to check out the "Classic" applications page for more options.
Finally, take a look at ALEMIA if you think you know that name of an application, but aren't quite sure.
No, I don't accept reviews anymore for these older applications. With the creation of this page in the Orchard's late 2005 redesign, I only accept reviews for currently-developed applications that work on Mac OS X (or later....whatever that might be!!).