A smart card operating system is characterized as being open if it is possible for third parties to load applications and programs into the smart card and run them in a secure environment, all without the involvement of the operating system producer. The three best-known open smart card operating systems are Multos, Java Card and Windows for Smart Cards. Open smart card operating systems are usually inter-operable, rather than proprietary. The term ‘open platform’ is also used to refer to an open smart card operating system, but it should not be confused with Open Platform (OP), which is an interface for managing applications in smart cards.