Linux - The Free OS
The first OS ever written was Unix - conceived 1969, born 1971 - not Windows. And it was not free. Minix came in 1987, was free, but was only for educational purposes, not commercial.
While the GNU Project - started in 1983 - thought of a GNU Kernel which was not ready even by 1991 - Linus Torvalds in the University of Helsinki became frustrated of MINIX's licensing and started writing his own Operating System. He names this Freax and rejected the name linux since it sounded too egotistical. He consented to the name of Linux when another person used it without his permission. More history...
Linux drew heavily from the open source GNU project. By 1996 Linux, the free OS was taking off.
By this time, Microsoft had taken the desktop market with its "paid" Windows OS, while Apple's Mac OS lagged.
The Linux kernel matured over time and by 2004, Ubuntu stormed in with popular desktop versions.
As of 2018, Ubuntu Linux is by far the largest OS in distribution with only rough estimates since not all installations can be tracked, since it is distributed free. More...
The usage of linux is from telecom systems - both towers and mobiles - to set-top boxes. Android of Google is built on Linux. Do we need to say more.
As we said, the best things in life are FREE.