SumatraPDF is a multi-format (PDF, EPUB, MOBI, FB2, CHM, XPS, DjVu) reader for Windows under (A)GPLv3 license, with some code under BSD license (see AUTHORS). Want to join the project and contribute code? Read https://github.com/sumatrapdfreader/sumatrapdf/wiki/Contribute-code To compile you need Visual Studio 2013 (free Community edition from http://www.visualstudio.com/en-us/news/vs2013-community-vs.aspx will work). Use vs/sumatrapdf-vc2013.sln.