nmon is described as 'This systems administrator, tuner, benchmark tool gives you a huge amount of important performance information in one go. It can output the data in two ways' and is an app in the OS & Utilities category. There are more than 10 alternatives to nmon for Linux, BSD, Mac, Windows and GNOME. The best alternative is htop, which is both free and Open Source. Other great apps like nmon are Glances (Free, Open Source), GNOME System Monitor (Free, Open Source), vtop (Free, Open Source) and Resource Monitor (Free).