Houdoku is a free and open source manga reader.
Library Extensions
Read series from popular manga aggregators or from your own filesystem, and manage them all in one place.
Customizable Reader
Read manga or webtoons with a configurable reader, including vertical and two-page reading modes.
Automatic Series Tracking
Automatically check for updates to series in your library, and save your progress as you read -- or sync with your AniList/MyAnimeList account.