Books 'N Bytes groups authors into specific categories.
Reader's Advice "genre index" groups very specific categories into the following broader categories:
Children's & YA | Family | Fantasy | General | Historical | Horror | Humorous | Military/War | Multicultural Fiction | Mystery | Notable Fiction | Religious/Spiritual | Romance | SF | Short Stories | Suspense/Thrillers | Western Clicking a category displays a list of authors who write in that category. The author index lists author's by last name, followed by a list of genres the author writes in. Clicking a genre retrieves a list of all authors writing in that genre and the books they wrote in that genre.
"BookBrowse" provides browsing by genre, time period, and theme.
SLIS Reading Group reviews books, i.e., describing each book's appeal and recommending other books like it.
"List of literary genres" in Wikipedia provides a long list of basic and subgenres. Clicking the genres displays a description of the genre mentioning prominent names and sometimes a list of authors who write in that genre.
"Lists of authors" in Wikipedia groups authors by genre, religion, nationality, race or ethnic group. Clicking groups retrieves the list of authors. Clicking the author's name retrieves articles about the authors.