1. A method of migrating applications to an application hosting cloud that hosts any applications for access by clients over the Internet, the method comprising: selecting a target application to migrate to the application hosting cloud, the application hosting cloud providing cloud-based virtual platforms wherein applications can execute as if on a hardware platform, the target application, prior to migration, configured to execute on a particular computer host platform; passing the target application to a migration tool, wherein the migration tool is provided with access to a rules library comprising one or more pluralities of migration rules, wherein each plurality of migration rules corresponds to a respective different application hosting cloud, and wherein the plurality of migration rules describe at least one of code rules, operating system rules, semantics rules, database rules, or installer rules; parsing and analyzing source files and configuration files of the target application with the migration tool to identify one or more migration rules from the rules library that are determined to be applicable to the target application, a migration rule configured to transform references to a particular network service to an analogous service provided by the application hosting cloud; and applying the identified one or more migration rules to the target application to generate a form of output to modify the source and configuration files of the target application from being configured for the particular computer host platform to being at least partly configured for the application hosting cloud.