I found this figure (edit: transcribed)
articlefor articles in scientific journals, presentations, short reports, program documentation, invitations, ...
proca class for proceedings based on the article class.
minimalis as small as it can get. It only sets a page size and a base font. It is mainly used for debugging purposes.
reportfor longer reports containing several chapters, small books, thesis, ...
bookfor real books
slidesfor slides. The class uses big sans serif letters.
memoirfor changing sensibly the output of the document. It is based on the
bookclass, but you can create any kind of document with it (1)
letterFor writing letters.
beamerFor writing presentations (see LaTeX/Presentations).
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.