Boorusphere - Yet another booru viewer for Android.
Imgbrd-Grabber - Very customizable imageboard/booru browser and mass downloader, with powerful filenaming features.
Booru Nav - an app designed for simple browsing at different anime imageboards.
LoliSnatcher - A booru client with support for batch downloading, written in Dart/Flutter for Android but may support more platforms in the future.
Flexbooru - A booru client for Android, support Danbooru and Moebooru.
Bulk Image Downloader - With Bulk Image Downloader you can download full sized images from almost any web gallery.