Comic reader software
Mac
Simple Comic (CBZ, PDF)
iBooks(PDF, built-in backups if you use iCloud)
Preview(PDF)
Astonishing Comic Reader(PDF, CBZ, Chrome)
Windows
Foxit(PDF)
Adobe PDF Reader(PDF, historically vulnerability heavy)
ComicRack(CBZ, Android and iOS syncing companion apps)
Mcomix(everything)
Astonishing Comic Reader(PDF, CBZ, Chrome)
MangaMeeya(PDF, CBZ, still works but is old!)
Linux
Mcomix(PDF, CBZ)
YACReader(PDF, CBZ)
Peruse(PDF, CBZ, perfect for KDE systems)
Astonishing Comic Reader(PDF, CBZ, Chrome)