Can a browser based application write to files on a local hard disk?

[Alex Hewitt]

Scenario: Need a web application which collects user data that needs to
be stored on the user's local hard disk. Which tools can do this?

I know that web site based applications are usually prevented from
writing to the user's local hard disk but I would prefer that any user
data be kept local to the user rather than stored on my web site. The
reasons are obvious - I don't want to be responsible for the user's data
and I'd like to be able to say "We don't have access to your private
information because we don't store it on our web site".

Ideas?

-Alex