Argtable3 is an ANSI C library that simplifies parsing GNU-style command-line options. It provides a declarative API to define your command-line syntax, and because it's built on the standard getopt library, it ensures 100% GNU-compliant behavior. Argtable3 automatically generates the error-handling logic and usage descriptions that are essential for any robust command-line program, saving you from tedious boilerplate code.