Beyond Compare - Beyond Compare allows you to compare files and folders.
Okular - Okular is a universal document viewer based developed by KDE.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.