These are some command line tools for Linux. All these tools have one thing in common, they all use the Linux Command Line Interface (CLI).
These tools are mainly useful for developers and sysadmins who use the linux shell on a daily basis.
If you are new to the command line, I recommend this course
Ranger is a console file manager for the X Window System / Wayland. It lets you browse your file system using just the cursor keys. It's great for viewing images too, pressing the right arrow on an image shows it.
ncdu is a disk usage analyzer just like du. But ncdu has a unique approach to this problem of disk usage.
ncdu is a disk analyzer for the command line. It scans your home directory and shows you how much space each directory takes.
unlike du, it uses an ncurses interface.
Lynis is an open source security auditing tool that tests the security defenses of Unix-based systems.
It scans the system locally or remotely and gives a detailed report on the system’s security, allowing you to well-informed decisions for system hardening.
Lynis is a security tool designed to test common system security. This includes controls, policies and procedures as well as the actual security mechanisms of the operating system itself. It helps you to answer those questions and gives you recommendations how to improve overall security of your systems.