1. A system for executing business logic extensions in a client application, the system comprising: a server platform operative to expose one or more server-hosted application services to the client application, to receive a request from the client application to perform one of the server-hosted application services and, in response to the request, to execute one or more business logic extensions on a server computer; and a client platform operative to expose one or more client-hosted application services to the client application, to receive a request from the client application to execute one of the client-hosted application services and, in response to the request, to execute one or more of the business logic extensions on a client computer.