The Essential Macleod is a comprehensive software package for the design, analysis, manufacture and trouble shooting of thin film optical coatings. It runs under Microsoft Windows 11 and 10 operating systems, both 64 bit and 32 bit. The program can handle coatings from rugates to ultrafast, from single-layer antireflection coatings to demanding color separation beamsplitters, providing all that is necessary for their design, analysis, production planning and even reverse engineering of a failed production attempt.