Applicable to Asset Banks prior to version 3.1532.
Users can download all assets in their original format (assuming they have download original permission on them) from a particular category by enabling the download all from browse functionality.
To enable this update the value of the application setting download-all-from-browse-limit so that it is a value greater than 0.
Whatever number you select will be used as the top limit in terms of the number of assets a user can download at once from a category (i.e. if you set it to 100 and the user clicks 'Download all' on a category that contains 200 assets then they will get a zip containing the first 100 assets that they have download original permission on).
Applicable to Asset Banks version 3.1535 and later.
The select from browse functionality has been enhanced to allow the selection of specific assets on the browse page, as well as all the assets in the category and is no longer restricted to downloading of original formats.