Acts as a mixing service or an online wallet. This service operates only through tor anonymization network. Funds transferred to the Fog get mixed with other users' funds. When requested, funds are paid out in multiple randomized transactions to further anonymize the source of money. Comission as of August 4th 2012 is chosen randomly between 1-3% on all deposits.
Warning: As of August 21, 2012 there is an uncorroborated report of issues with the service. Use at your own discretion. Further information available in the forum thread for Bitcoin Fog (see External Links below).