That's an amalgam of two seemingly disparate acronyms; this bleeding edge technology is designed to help those of the "Y Chromosome" set more effectively and pleasantly interact with those who sport the "Double X." Specifically:
"PMSbuddy.com, a free Internet-based service that tracks the monthly cycles of a subscriber's significant other and offers e-mail reminders about the impending deadlines."
Modeled after other social networking sites (e.g. Twitter, FaceBook, etc), this may be the ultimate expression of MySpace. And it's certainly swelling: enrollment topped 150,000 last month, of which almost 15,000 are of the aforementioned "Double X" persuasion (although those numbers may be padded).
Although the service started off using email technology, founder Jordan Eisenberg has upped the ante by introducing a phone-based PMSsaging system, as well. The purported demographic for the site is men aged 20 to 40. But as mentioned above, a lot of females are using it, too; Eisenberg warns, though, that this method isn't for tracking fertility.