An application producing method regarding a first application and a second application, the method comprising: receiving, using at least one processor, an application generation request related to the second application, the second application being subordinate to the first application; generating, using the at least one processor, the second application and switch interface computer readable instructions related to a switch interface for selecting at least one of the first and second applications, the switch interface computer readable instructions, when executed by at least one application executing apparatus having a display unit, cause the at least one application executing apparatus to, display a first application image of the first application and a second application image (374a, 374b, 374c) of the second application simultaneously wherein the first application image and the second application overlap in a region of the display unit, display the switch interface (378a, 378b, 378c) on at least one of the first and second application images, control the state of the switch interface based on a switch interface user input received by the at least one application executing apparatus, adjust a transparency setting of the second application according to a state of the switch interface, determining the state of the switch interface to be in the first state when the transparency setting of the second application is higher than a transparency reference value; and determining the state of the switch interface to be in the second state when the transparency setting of the second application is lower than or equal to the transparency reference value, receive a first user input, and control one of the first application and the second application based on the state of the switch interface as follows: when the switch interface is in a first state, the first application is controlled based on the first user input, and when the switch interface is in a second state, the second application is controlled based on the first user input, and maintain an active state of the first application after the state of the switch interface is changed from the first state to the second state; and sending the generated second application and the switch interface computer readable instructions to the at least one application executing apparatus. receiving, using at least one processor, an application generation request related to the second application, the second application being subordinate to the first application; generating, using the at least one processor, the second application and switch interface computer readable instructions related to a switch interface for selecting at least one of the first and second applications, the switch interface computer readable instructions, when executed by at least one application executing apparatus having a display unit, cause the at least one application executing apparatus to, display a first application image of the first application and a second application image (374a, 374b, 374c) of the second application simultaneously wherein the first application image and the second application overlap in a region of the display unit, display the switch interface (378a, 378b, 378c) on at least one of the first and second application images, control the state of the switch interface based on a switch interface user input received by the at least one application executing apparatus, adjust a transparency setting of the second application according to a state of the switch interface, determining the state of the switch interface to be in the first state when the transparency setting of the second application is higher than a transparency reference value; and determining the state of the switch interface to be in the second state when the transparency setting of the second application is lower than or equal to the transparency reference value, receive a first user input, and control one of the first application and the second application based on the state of the switch interface as follows: when the switch interface is in a first state, the first application is controlled based on the first user input, and when the switch interface is in a second state, the second application is controlled based on the first user input, and maintain an active state of the first application after the state of the switch interface is changed from the first state to the second state; and sending the generated second application and the switch interface computer readable instructions to the at least one application executing apparatus. when the switch interface is in a first state, the first application is controlled based on the first user input, and when the switch interface is in a second state, the second application is controlled based on the first user input, and maintain an active state of the first application after the state of the switch interface is changed from the first state to the second state; and sending the generated second application and the switch interface computer readable instructions to the at least one application executing apparatus.