MuPDF viewer

Lightweight document viewerAGPL-3.0-or-later

MuPDF mini

Minimalist viewer for PDF, XPS, CBZ, unprotected EPUB, and FB2 documentsAGPL-3.0-or-later

Orion Viewer - Pdf & Djvu

Orion Viewer is pdf, djvu, xps, tiff and comic books (cbr, cbz, cbt) file viewerGPL-3.0-or-later

Librera Reader

Book and PDF readerGPL-3.0-or-later