Skim is a PDFreader and note-taker for OS X. It is designed to help you read and annotate scientific papers in PDF, but is also great for viewing any PDF file. Skim requires OS X 10.10 or higher.
chmosx is a chm reader for Mac OS X 10.5 (Intel). Main features: Multiple ways to navigate the pages in a chm document. Search document or page. Full screen support. Apple Remote Control support. Bookmarks manager. Tabbed documents. Converter to PDF