Call Studio is the development platform used to build VXML applications. It is a graphical development environment that allows developers to quickly build and deploy voice applications using drag-and-drop components. Call Studio comes with a suite of tools and components that allow developers to create interactive voice applications that can respond to user input and make decisions based on the input. Reference: https://www.cisco.com/c/en/us/products/unified-communications/call-studio/index.html