See, it's not intended for women, it's intended for the men who have to "put up" with them at "that time of the month."
Here's the site's own description: "PMSBuddy.com is a free service created with a single goal in mind: to keep you aware of when your wife, girlfriend, mother, sister, daughter, or any other women in your life are closing in on "that time of the month" — when things can get intense for what may seem to be no reason at all."
Yeah. Or maybe things get intense because you're the kind of guy who puts stock in services like PMS Buddy.
Am I missing the joke? Weigh in below.