YACReader - Download YACReader for your platform. Windows, Linux, MacOSX. And enjoy you comic books cbr cbz with the best comic reader.
Boorusphere - Yet another booru viewer for Android.
Tachiyomi - A free and open source manga reader for Android.
Imgbrd-Grabber - Very customizable imageboard/booru browser and mass downloader, with powerful filenaming features.
Mcomix - MComix is an user-friendly, customizable image viewer.
LoliSnatcher - A booru client with support for batch downloading, written in Dart/Flutter for Android but may support more platforms in the future.