Zip mime types, when to pick which one

I don't know of any existing script that would classify these types as you wish. You may need to create this function yourself based on the distinctions you require, e.g. application/msword -> office rather than application, etc.

As your classifications are fairly arbitrary and particular to your own use-case, you'll likely have to classify them yourself into your desired categories, e.g. by using a function something like the below:

/**
 * Classify mime types into pre-determined categories
 * 2-d array used for simplicity of example, error
 * checking omitted so unrecognised string returns
 * empty value here...
 */
function categorize_mime_types($mime)
{
    // Classify mime types into desired categories, key-val pairings
    $mimes = array("application/msword"=>"office",
                   "application/vnd.oasis.opendocument.text"=>"office",
                   ....
                   "image/jpeg"=>"image");
    return $mimes[$mime];
}

Collecting all of the mime types to do this could be quite time-consuming, although there are a number of website which have large lists to get you started.

You should send the file with, ensuring the file extension is included:

Content-disposition: attachment; filename=Test.zip

As a header.

In C#:

Response.ContentType = "application/zip";
Response.AddHeader("Content-Length", contentLength.ToString());
Response.AddHeader("Content-disposition", "attachment; filename=" + fileName);

if (Request.UserAgent.Contains("MSIE"))
{
    Response.AddHeader("Content-Transfer-Encoding", "binary");
}