System, method, and API for progressively installing software application

Described is a mechanism for enabling an application operating as a web application to transition to a client-side application without impacting a user's interaction with the application. The progressive installation transitions through three states: a start-up state, a demand state, and an install state. During the start-up state, a subset of components associated with the application is downloaded and stored in a local data store. The subset is sufficient to allow execution of the application in a manner similar to a web application. During the demand state, additional resources associated with the application are downloaded. Transitioning from the demand state to the installed state occurs without impacting a user's interaction with the application. The transition may occur autonomously based on the number of additional resources stored in the local data store or upon an external trigger.