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.
Flexbooru - A booru client for Android, support Danbooru and Moebooru.
Ahoviewer - A GTK2 image viewer, manga reader, and booru browser.
The Wolf's Stash - An app to easily browse the content on e621 and e926!