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

Fast PDF, DjVu, XPS, TIFF and comic book (CBZ, CBR, CB7, CBT) viewerGPL-3.0-or-later

Librera Reader

Book and PDF readerGPL-3.0-or-later