NeoDownloader - As you know, there is a lot of websites with a lot of pictures, music and movies.
Boorusphere - Yet another booru viewer for Android.
Vov Picture Downloader - Download pictures from websites.
Imgbrd-Grabber - Very customizable imageboard/booru browser and mass downloader, with powerful filenaming features.
Bulk Image Downloader - With Bulk Image Downloader you can download full sized images from almost any web gallery.
LoliSnatcher - A booru client with support for batch downloading, written in Dart/Flutter for Android but may support more platforms in the future.