htop is an interactive process viewer which runs in the terminal. It shows all running processes with additional information like PID, user, CPU-usage, memory etc. It also has some graphical meters for CPU, memory, swap etc. It is customizable in many ways, you can scroll through the process list, change the viewable columns and meters and also kill selected processes.
Install htop with
sudo apt-get install htop
and the processes are shown in the terminal
To quit htop, F10 is used. Since the terminal in Ubuntu uses F10 to access the file-menu, htop can be quit by using Ctrl+C