Personnummer is a ruby class that handles [Swedish personal identity number](http://en.wikipedia.org/wiki/Personal_identity_number_(Sweden\)).
$ gem install personnummer
>> p = Personnummer.new('830428-5912') => #<Personnummer:0x301128 @number="830428-5912", @age=25, @valid=true, @region="Skaraborgs l\303\244n", @male=true, @born=#<Date: 4890905/2,0,2299161>> >> p.valid? => true