20 Great Terminal Replacements for GUI Applications

Process viewer: htop
htop is an improved version of top, a complex process viewer which allows to visualize processes in real time, see memory and CPU consumption, send signals to processes, renice processes, and sort them by various options. It makes use of colors and you can also scroll horizontally and vertically to see the full names of the running processes.

Image viewer: cacaview
This is an ASCII image viewer for the terminal with support for all the popular image formats like JPG, PNG, GIF or BMP.