The W3C's Web Applications WG (WebApps) created a suite of specifications related to packaging Web applications. This set of specs (briefly described in Widget-Specs and sometimes called "W3C widgets"), are mostly complete as documented in Widget-Pubstatus.
One use case of WebApps' packaging spec is installing an application for offline or online use (the spec itself makes no distinction on those two classes of applications, nor does the application need to be a "Web application"). There are of course other ways to manage and package Web applications for offline usage, and references to some of them are included in WebApps' Embedding-wiki.
I support the W3C doing work that identifies high priority use cases and interop issues, analyzes prior related spec work, reviews the various non-standard implementations/deployments, identifies standards gaps, etc. with the overall goal of creating standards that reduce fragmentation in this area.
WebApps has a "Widgets Embedding" deliverable in its charter WebApps-Charter that is arguably related. However, since no formal work has been done on that deliverable, it would probably be better if a new more focused effort was started.
-Art Barstow (Co-Chair of WebApps WG; speaking on behalf of himself and not his employer nor WebApps WG)