Free Operating Systems
Most of the listed Operating Systems are Open Source and you can get ISO images of so called Live systems which could be used by everyone who know how to burn ISO images and to boot up the computer from CD/DVD or other bootable media like USB flash drives. You can also create bootable USB-Sticks and Windows Live Systems (WinPE) or start a Linux image under Windows thru the program MobaLiveCD and other tools. Read more some lines below!
Linux Operating Systems
is an often used and popular Ubuntu and Debian respectively, derivative. It works very well, is easy to install, easy to use and it looks really pretty. The Mint MATE start menu could be replaced easily with the splitted or the well-known standard menu from GNOME 2. When you start the system for the first time after installation you'll see a welcome screen which provides a list of features and a user guide in PDF. Featured Linux Mint Editions: Mate (GNOME 2 based) 32/64-bit, Cinnamon (GNOME 3 based) 32/64-bit, Xfce 32/64-bit), KDE (32/64-bit) and LMDE = Linux Mint Debian (Mate and Cinnamon, Xfce, 32/64-bit). Advantage of 64-bit: No RAM limitation which is only important if you have more than 3 GB of RAM and a 64-bit compatible CPU. Otherwise, use the 32-bit edition!
Screenshots: MATE and Cinnamon.
Mint has a large community with Wiki, Forum aa well as local Websites and Forums. Furthermore you'll find informations about Desktops and Laptops with Mint preinstalled and the mintBox. Find more about Linux pre-installed near the bottom of the page!
Visit the Mint Homepage to get all those informations.
Download the ISO image, burn a CD and start working with Xubuntu. AbiWord for text processing, Gnumeric for working with spreadsheets, an image viewer and GIMP for advanced image editing, a reader for PDF documents, the web browser Firefox, the eMail Client Thunderbird and some more applications are already integrated. Additional programs like the FTP client FileZilla could be installed from the large online repository thru using the Software Center or Synaptic the Package Manager.
You can use Xubuntu (32/64-bit) on PC's, Notebooks as well as Netbooks.
Here is a Screenshot for you.
Visit the Xubuntu Homepage, download, burn and explore your new Operating System!
Visit the Ubuntu Homepage and discover other derivatives like Ubuntu MATE!
Linux Mint and Xubuntu are ready for the efficient and everyday use and also recommendable for beginners and people who want to switch from Windows! Cause you get Live-CD/DVD you can test the system first and if you want you can install it after testing enough. Just click on the icon in the upper left corner and you'll be supported with a graphical install wizard in many languages. If you have a Windows system installed on your machine: Don't worry! You only need enough free space on your hard drive. After the installation process is done, you have to reboot and chose (up and down arrow keys) between Linux and Windows.
Linux Lite - Based on Ubuntu with Xfce like Xubuntu but with it's own nice tools and LibreOffice instead of AbiWord and Gnumeric. Firefox, Thunderbird, VLC video and music player, an image viewer, GIMP for image editing, Xfburn for CD/DVD burning, PDF viewer and more apps are included. Additional software is available and easily installable.
Until this point I can recommend the featured Systems without any restriction for installation (also beside existing Windows systems) and for the efficient and everyday use for Linux newbies, cause these OS are really easy to install and to use! Naturally this applies also to Debian which is the base of Ubuntu and many other Linux based OS and don't forget to have a look at Devuan!
From this point on, the systems are more recommendable for advanced users!
KNOPPIX - The first time I used this great Debian based live system from Klaus Knopper was in 2004 and I found it to be very useful. Since ADRIANE started with KNOPPIX 5.3, the distro is also very recommendable to partially sighted and blind users. You can run the Live-CD (Screenshots) also embedded under Windows thru qemu! KNOPPIX works with the pretty looking LXDE (Lightweight X11 Desktop Environment). It's not only fast, it also eats less memory and CPU than other environments like KDE and GNOME do!
Bodhi - Ubuntu based system for Desktops, Laptops and Netbooks (also Chromebook).
4MLinux - Little OS (ca. 700MB), with various useful and yet smaller editions.
Porteus - Also a good and little system (from tight under 200MB until tight over 400MB) with various editions for Desktops, Notebooks and Netbooks, CDs and flash-drives.
Puppy Linux - Small OS (ca. 350MB) which is easy, fast and good for normal Computers, Notebooks, CDs and flash-drives. Screenshots of Puppy Tahr (Ubuntu repositories).
SliTaz - Very small (ca 50 MB) but powerful and will load completely in your computers memory if there is enough RAM available. After SliTaz has fully loaded, remove the Live-CD and use the device e.g. for burning a data or audio disk or to save data if you use a pen-drive. Add the applications you like thru the package manager, configure the programs and the system like you want and write a new ISO or put your new SliTaz onto an USB flash drive!
Secure, incognito Live OSs: heads and Tails.
ONLY browsing systems: Porteus Kiosk - Webconverger
Rescatux and Super Grub2 Disk - Start systems with corrupt or broken bootloader, recovery and repair operations on Windows, Linux, Mac and FreeBSD, 32/64-bit machines.
Systems for Kids
Sugar on a Stick (SoaS) - OS for Kids installable on USB flash drives.
DoudouLinux (Live-CD/USB) - Based on Debian for Children from 2 to 12.
PicarOS - System for Kids from 3 to 12.
Pupils and Students
DebianEdu - is an educational system for schools and pupils at home which is really easy to install and to use. It's directly based on Debian and works with the K desktop environment (KDE). The network interface is pre-configured so that you can set up a network without advanced knowledge about (Linux) network technology.
Edubuntu - Another system for pupils and students.
UberStudent - Learning and teaching for students and learning institutions.
Mobile Operating Systems
Ubuntu Touch - Try it if you have a Fairphone 2 and consider to buy a Fairphone 2 if you want a cool and fair Smartphone. Other phones are also supported by Ubuntu Touch.
Advanced useres ONLY, make a backup to external device, first!
Phoenix OS works on normal Computers, Tablets and Notebooks.
LineageOS supports really a lot of phones.
Sailfish OS is another good alternative to Android.
Android itself is also available for "normal" computers: Android-x86
AndEX - Custom Android-x86 from Exton Linux, also available for Raspberry Pi.
Why Linux? Cause Android is Linux based!
There are also alternative Appstores out there:
Best choices for Android (pure apk files, no store file download and install, no registration):
Getjar - 1Mobile - APKMonk
Android (Registration): SlideME - Aptoide.
iOS: Sorry, couldn't find a good one.
As you can see, there are some very good Operating Systems which you can download and use without of charge and it's mostly Open Source. Why buy expensive ones??? If you didn't find it here, I'm sure you'll find a system which fits your needs at Distrowatch, where you'll also find a list with vendors where you can buy computers with Linux OS pre-installed.
More lists with vendors:
Desktops, Laptops and Servers: System76
Desktops and Laptops: ThinkPenguin
Notebooks, PDAs and Mobile Phones: TuxMobil
Desktops and Notebooks: LXer
Vendors that sell computers with Debian pre-installed.
If you need help, visit the Linux Forum!