How to upload multiple files using one file input element

I'm using possibility to send array of files. Just add [] to name atrribute:

<form action="/" enctype="multipart/form-data" method="post">
    <input type="file" name="files[]" />
    <input type="file" name="files[]" />
    // etc.
    <input type="submit">
</form>

You will have array of arrays in $_FILES

Array
(
    [files] => Array
        (
            [name] => Array
                (
                    [0] => 1.png
                    [1] => 2.png
                )

            [type] => Array
                (
                    [0] => image/png
                    [1] => image/png
                )

            [tmp_name] => Array
                (
                    [0] => /tmp/phpDQOZWD
                    [1] => /tmp/phpCELeSw
                )

            [error] => Array
                (
                    [0] => 0
                    [1] => 0
                )

            [size] => Array
                (
                    [0] => 32209
                    [1] => 64109
                )

        )

)

Of course, you you'll have to upload them one by one. Not convenient to a large number of files, but works in all browsers. For example,using jQuery you can add one more input each time last files[] input was changed.

function addOneMoreInput() {
    $('input[type=file]').last().change(function() {
        $(this).after('<input type="file" name="files[]" />');
        $(this).off('change');
        addOneMoreInput();
    });
}
addOneMoreInput();

The multiple file select in the dialog when you click on the browse button of the file field happens only for the new browsers supporting HTML5. It wont allow multiple select for old browsers. For older browsers the only good solutions are flash or javascript plugins. Here is a good resource for jquery uploaders ( some support multiple files ): http://creativefan.com/10-ajax-jquery-file-uploaders/. Hence my suggestion is use some plugin so that its supported on old as well as the new browsers.