MuPDF is a lightweight, fast PDF and XPS viewer capable to run on multiple platforms, including Android and iOS. It also includes its own `fitz` rendering library.
MuPDF started its life somewhere in Scandinavia, but then it was adopted by the Ghostscript community. Since then it was nursed in the cradle of the Ghostscript developers and brought to life as a lightweight PDF viewer, meant as an alternative to Ghostscript. Recently it gained XPS viewing capabilities too.
It serves as the core for the popular lightweight and fast SumatraPDF viewer on Windows, but it is ported to many other platforms too (including Android and iOS).
In its core is its own fitz
rendering library.
MuPDF's implementation of PDF-1.7 features is rather complete: it supports transparency, encryption, hyperlinks, annotations, searching and more.
From the 1.2 release of MuPDF, there is optional support for interactive features such as form filling, javascript and transitions.
License: AGPL v3 or commercial (from Artifex)
Sources: git clone git://git.ghostscript.com/mupdf.git
Contact: MuPDF developers hang out on IRC in the #mupdf
channel on irc.freenode.net.