An install program. Installers are programmed/customized by the developer to fit the application requirements. Their primary purpose is to compress the application files into one or more self-extracting files that decompress into the appropriate folders when run. They also make modifications to the Registry in the user's PC and provide post-install options such as the capability to run a program. Commercial installers are comprehensive and sophisticated and may support a full-blown programming language or provide their own scripting language. See install program.