Facebook claims that it is not possible to check all who have viewed or visited your profile, but there are some applications which enable you to find out the profile visitor. How does this work?
As Sathya says, these apps are fakes. Even apps that claim to make your visitors look like stalkers are fake. Never trust any app that claims to do this.
Most either fake the numbers, or use data collected from other people using the app (aka they ask your friends to join as well). Stalking apps just display the person's name - nothing clever.