htop

Task manager. Shows CPU/Mem usage.

bpytop

Bigger fancier task manager.

powertop

Shows power usage, but is rather confusing about it.

bwm-ng

TUI program for showing active network usage.

viddy

Watch the output of a process.

entr

Run a command when a file changes.

dmesg

Print or control the kernel ring buffer.

lsusb

List all usb devices.

lswh

List information about your hardware.

hwinfo

Another hardware info tool.

lscpu

Print out very detailed cpu information, including vulnerabilities.

lsof

List open files.

strace

Print system calls a program makes.

ltrace

Print dynamic library calls a program makes.

fatrace

Show all file open/read calls.

objdump

Print information from binary object files.

collectd

The system statistics collection daemon.