ACD/ChemSketch is described as «chemically intelligent drawing interface that allows you to draw almost any chemical structure including organics, organometallics, polymers, and Markush structures. Use it to produce professional looking structures and diagrams for reports and publications» and is an app in the education & reference category. There are more than 10 alternatives to ACD/ChemSketch for a variety of platforms, including Windows, Mac, Linux, iPhone and iPad. The best alternative is Chemaxon Marvin, which is free. Other great apps like ACD/ChemSketch are Avogadro, BKchem, ChemDoodle and Gnome Chemistry Utils.