Reads html, rtf, txt. Preserves inline html links, reformats paragraphs. Saves the index of the read books. Allows reading from rar or zip files, by a best file-match (first html variants, then rtf then txt). Download books from Project Gutenberg, and covers from OpenLibrary.
If your ebook files are divided into many sub-files or in a format that the reader doesn't read use calibre to convert (mobi or epub can be converted to htmlz and that works).