1. One or more computer-readable memories storing computer-executable instructions that, when executed by one or more processors, configure the one or more processors to perform acts comprising: storing a portable database including metadata for a portable application on a portable storage device, the metadata included in the portable database being unavailable from a system database of system metadata on a computing device that accesses the portable storage device, each of the metadata and the system metadata affecting at least one functionality or at least one behavior of the portable application during execution by the computing device, wherein the portable database is accessed or loaded from the portable storage device, and the at least one functionality comprises a customization to the portable application enabled by the metadata in the portable database; executing the portable application stored on the portable storage device; intercepting a request for relevant metadata from the system database via an intermediary component; determining whether the relevant metadata exists in the portable database; reading the relevant metadata from the portable database using the intermediary component without reading the system metadata from the system database in response to determining that the relevant metadata exists in the portable database; and supplementing the portable database to create a combined database by reading the metadata from the portable database and the system metadata from the system database.