Some of the available classes of documents in LaTeX are well known and widely used, such as the
beamer classes, while others are not so well known, such as the
I found this figure
which lists the main classes and is a good starting point, but the description is too short and still leaves one wondering when it would be more suitable to choose one class over the other and what the characteristics of each class is. Furthermore, the list is not exhaustive I think, given that I know at least one more document class that is not there (the
standalone class, as I mentioned).
So my question is: what are the available classes of documents in LaTeX, and could you provide a brief description of the class and the situations where it would be recommended?
Please give only one class per answer.