<p>I have a number of users with multi-megabyte files that need to be processed before they can be uploaded. I am trying to find a way to do this without having to install any executable software on their machines. </p>

<p>If every machine shipped with, say, Python it would be easy. I could have a Python script do everything. The only scripting language I can think of that's on every machine is JavaScript. However I know there are security restrictions that prevent reading and writing local files from web browsers. </p>

<p>Is there any way to use this extremely pervasive scripting language for general purpose computing tasks?</p>

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<p>EDIT: To clarify the requirements, this needs to be a cross platform, cross browser solution. I believe that HTA is an Internet Explorer only technology (or that the Firefox equivalent is broken).</p>

The application that I maintain and develop for work is an
HTML Application
or
HTA
, linked with a SQL Server 2005 backend. This allows various security restrictions to be "avoided". All the client-side components in the application are done with javascript, including writing files to locally mapped network drives and loading data into screens/pages in an AJAXy way.
Perhaps HTA could be helpful for your situation.