It's easy, you put your address email in the, eventually a text (not too long) and go. The email address is not stored or used (in fact you can put any string you want). If you lose your card, just come back here, re-enter your mail address and you'll get the same card.
It uses a CRC32 of your mail address to seed a pseudo-random number generator which will generate your card. It's still here for people who have generated a card with it.
Version 2 has PRNG and CRC function embedded. For CRC it uses http://en.wikipedia.org/wiki/Adler-32 as found on wikipedia and for PRNG it uses example shown in man 3 rand.
As Adler-32 is said to be not good on “few hundred bytes”, the program add 32 times xored (with hand picked values) mail address to calculate the CRC, so for a normal email address it has ~600 bytes of data.
License is WTFPL 2.0.