Without a browser is a bit nebulous ... but I'll tell you what I'm
doing and you can judge for yourself whether it meets your
requirements.
If you create the proper manifest, a web-application can be stored on
the user's hard-drive and run while off-line. I use Mozilla's Prism
as the "non-browser" ... it looks just like the application in a web
browser but has no navigation controls. Once you've got an off-line
application running, you'll also need to store the data locally. This
is only a little bit harder thanks to HTML5. Use the localstorage
calls in the Javascript engine to allow storage to the local hard-
drive. Note that this storage is a map controlled by the browser, so
you can do rudimentary indexing if you're smart about picking your
keys, but you do NOT have complete access to the local hard drive and
the total amount of storage allocated is limited by Prism (but can be
expanded by the user).
Here's a link to get you started with both off-line application
caching and localstorage:
http://www.w3.org/TR/offline-webapps/
Hope this helps!
smoyer