I used a few, such as ReactOS and other Windows clones, but they all seemed poorly resourced and, above all, the general impression is that they are still immature.

ReactOS, Haiku and some BSD (UNIX)

It would be necessary to delimit what is meant by free, free to use (without paying a fee), free to modify like GNU Linux.

No in my case I don't know any operating systems other than Windows, Linux, MacOS.

Now if you talk about Linux distributions it is different there are use a lot a great majority were about more visually appealing distributions.

If you talk about Linux distributions it is different there are use a lot a great majority were about more visually appealing distributions.

A few years ago I used FreeBSD in the context of a computer security course I gave to some colleagues. Anyone familiar with Unix OSes and the like will find themselves at home on FreeBSD.

I also dabbled, more years ago, with the Hurd kernel of the Debian distribution. Just for the sake of experimentation. I found it complex to install and configure, and ended up leaving it behind.

Several in 20 years but always remain halfway, for lack of software or drivers, the only one I see with future is the prox. S. O. google Fuschia as I consider google the King of programming, also will be multi-platform PC-mobile and Android.

First of all, Linux is not an operating system, it's just a kernel. It's mostly used in conjunction with GNU tools, so I assume you mean the GNU/Linux operating system, in any of its distributions.

Yes, I've used Android a lot, which at its core is a free operating system, and I've also been trying out ReactOS, a free implementation of Windows.

I've also been trying out ReactOS, which is a free implementation of Windows.

I've merely been using Slackware, which is quite strange to install and configure...

I've been using Slackware, which is quite strange to install and configure...