This is GNU patch, which applies diff files to original files.

This version of patch has many changes made by the Free Software Foundation.
They add support for:
 * handling arbitrary binary data and large files
 * the unified context diff format that GNU diff can produce
 * merging into files instead of creating reject files
 * making GNU Emacs-style backup files
 * improved interaction with RCS and SCCS
 * the GNU conventions for option parsing and configuring and compilation.
 * better POSIX compliance
They also fix some bugs.