File identification software


 * DROID (cross-platform, open source, website): "DROID is a software tool developed by The National Archives [of the United Kingdom] to perform automated batch identification of file formats." Requires Java 6, will not run on Java 7 as of 28 Oct 2012.
 * File command (various implementations): a standard Unix command, found on almost all Unix and Unix-like (i.e., Linux) systems. See the manual page for the Debian version for an overview.