htop - htop - an interactive process viewer for Unix. This is htop, an interactive process viewer for Unix systems. It is a text-mode application (for console or X terminals) and requires ncurses. Latest release: htop 2.
Okular - Okular is a universal document viewer based developed by KDE.
gtop - System monitoring dashboard for terminal
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
nmon - This systems administrator, tuner, benchmark tool gives you a huge amount of important performance...
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.