I've heard some good things about Puppy Linux. It's around 100 MB, and it comes in a portable version too, so you can test it out first. I haven't tried it myself, but it seems good if you want something small & fast.
It all depends on the distro. I use the live cd version of Backtracks for security audits. I have also used Ubunto that also has a live version so, nothing to install. I boot off of my usb thumb drive.
Kali Linux for security
WiFISlax for wifi security audit (live cd)
I recommend to use debian and gnome interface or another, however there linux ah well light as the puppy already quoted, and "dawn small linux" and some lighter still as "tiny core" that runs on very old machines with only 50mb of ram and hd 200mb kkkk
Here is the thing with lighter distro's. They have next to nothing installed. You will have to add things that you want to use and may need to update things.
As for Kali, I recommend staying away from it. Its buggy and crashes a lot. It has too many young kids trying to make it l33t and it doesn't work. It was a replacement for Backtracks, but failed big time. Its more like windows then an actual linux distro.
I am using puppy linux and archlinux. Both are good. Puppy linux is very compact but if you want to various things, sometimes it may be suitable. Archlinux is very flexible and you can setup one by one , then you can avoid to install unnecessary modules at all . I personally recommend it.
Gentoo if you can get it installed and configured. Nothing extra whatsoever, you install only what you want.
I've heard good things about Arch, but I haven't used it. Debian is light enough depending on what you install. I use Debian / KDE on desktop, Debian / XFCE if it's got to be light.
For a lightweight Linux operating system I believe you must try the Ubuntu Deriavatives Xubuntu and Lubuntu as they both are known to pump life into aging old systems with hardware not capable of running conventional Operating systems such as Windows and/or heavier linux kernals such as Debian, Ubuntu Stable and Fedora.
You can do something like a minimal install with debain and only install the applications you need for a very small installation. I tend to look for a balance between useability and resource usage and currently using lubuntu.
Of course there are always Puppy, Damn Small Linux, and similar projects (you could search for them on distrowatch!) - but in case you're wondering, there's something ELSE. There are ASM (assembler) based operating systems; that weights as little as 1.44 megabytes (1 floppy drive!) and has GUI and coding IDE, some small 3D games and more! These OS are:
* Menuet OS
* Kolibri OS
There's also a pick of other small operating systems, such as:
* React OS
* RISC OS
They are in some sort similar to linux and interesting to learn. PM me if you have any questions & good luck!
I don't quite understand your question "In your opinion, what is the linux os less heavy in the world?"
Let me rephrase your question.
"In your opinion, what Linux OS is the lightest in the world."
In this case, I would think that TinyCore is the lightest Linux OS in the world. It actually comes with basic bash/ ash support and some useful important applets. It doesn't have any GUI (Graphical User Interface) and only has a command prompt when you boot into the OS.
You also have to install the OS manually by using commands like fdisk and many more. You also have to maybe copy the OS files to a partition (for your OS).
If you want to surf the Internet, you only have one network access choice, which is... Ethernet. Yup, Ethernet. You have to install drivers yourself because this is a minimal OS. Even the process of installing drivers are very hard, complicated and may fail easily.
What about installing a GUI (Desktop). Many users use OpenBox for this OS. A window manager is already more than sufficient to use GUI applications. Same as the network part, installing it is already very hard, complicated and may fail easily.
As conclusion, this is what I think is the least heavy OS in the world.
I really like linux, especially the bootable cds. I am currently using windows though I would definitely recommend linux.
If we're talking about computer resources, I'd argue Arch Linux to be very lite, mostly because it's a very bare bones when freshly installed. And you can customize and add on to it what ever you desire. It's honestly perfect for my raspberry pi, which runs headless and doesn't need all that much, let alone a GUI. Though you do have to have some advanced knowledge of Linux to be able to install it, and configure it properly.