- The Grand Unified Debugger (GUD) in Emacs is an underappreciated built-in feature that supports multiple debuggers like GDB, LLDB, Perl, Java, Python, and others.
- A demo using GDB with a Fibonacci program shows how to set breakpoints via fringe clicks, use toolbar buttons (Run, Next Line, Step Line, Up/Down Stack), and manage breakpoints in a dedicated window.
- GUD provides features like an I/O window for output, variable inspection by hovering, a locals window, and variable watching for automatic updates when values change.