For macOS and Linux/Unix, try Calibre. Use ComicScreen to open CBR files on Android, and icomix to open CBR files on iOS. Alternative readers to try are SumatraPDF, which is also free, or CDisplay Comic Reader. The default program for opening CBR is CDisplay Ex, which is free, popular, and can read other comic book file formats. CBR files are also known by the more simple term, Comic Book Reader file.
In reality, it is a Roshal Archive Compressed (RAR) file but renamed to CBR to distinguish it as a file that contains comic books. CDisplay RAR Archived Comic Book (CBR) is a compressed file type that can contain many different files stored together to form a single archive file of digital comic books.
