If you've got someone's first name, it's possible to make a pretty accurate guess what their gender is. Obviously there's plenty of exceptions, Sean and Francis spring to mind, but for lots of applications you don't need 100% accuracy or coverage. In my case I want a better understanding the demographics of my users, so a figure that's within a few percent is fine.
There's a great Perl module called Text::GenderFromName that implements this idea, with accumulated wisdom dating all the way back to a 1991 awk script! I haven't found anything that fits well into my PHP projects though, so I finally bit the bullet and ported that Perl script to PHP. The result is up at
and you can get the source at
For best results you should also install the doublemetaphone PHP module, though it will function without it.