BleachBit - When your computer is getting full, BleachBit quickly frees disk space.

nmon - This systems administrator, tuner, benchmark tool gives you a huge amount of important performance...

CCleaner - CCleaner cleans, speeds up and frees up space on business endpoints.

iftop - iftop does for network usage what top(1) does for CPU usage.

Tron Script - Tron is a glorified collection of batch files that automate the process of cleaning up Windows systems.

vtop - vtop is a graphical command-line tool that uses unicode braille to chart CPU and memory usage.