It is easy to replace one design with another and people want to be unique in this aspect anyway.If someone would create a calendar app, and you would like to r

It is easy to replace one design with another and people want to be unique in this aspect anyway.If someone would create a calendar app, and you would like to replace it with another, its perfectly fine if visually they would be slightly different. Copyright and design patents do not block ability to create functional equivalents, because people do not rely on design being exactly the same. API's are different. If you provide an API, then all clients must use exactly the same "design"(function names, arguments, error codes, everything). If someone else would want to provide alternative implementation, they can not change anything, otherwise clients will stop working and need to be changed. So the concepts may be similar, but implications are entirely different.