Debian

A free, volunteer-built operating system that many servers and other Linux systems are built on.
Debian is a free operating system built by a worldwide group of volunteers, started in August 1993 by Ian Murdock. Like Ubuntu, it’s a version of Linux: the software underneath a server that keeps it running. There’s no license to buy, and no single company owns it.
People choose Debian when steady matters more than new. Its own site describes it as stable and secure, with security support for each stable release and a long term support effort that keeps every stable release going for at least five years.
Debian also has a wide family tree. Ubuntu is one of several systems built on its work. You won’t see any of this as a website owner. It simply sits under the web server and database, quietly doing its job, and a well-run Debian server rarely needs attention.
Why Debian Is in Our Stack
In Practice
Debian is in our toolbox as a calm, proven choice for servers, and the system Ubuntu grew out of. We reach for it when a project wants a minimal, long-lived server and the hosting provider supports it.
Built to Last
Stable releases get security support, and the long term support effort covers at least five years.
Free and Independent
No company owns it, and there's no license fee to pay.
Proven Foundation
Other systems, including Ubuntu, are built on Debian's work.