Debian 9 codenamed "Stretch" is the version of the Debian operating system that was released in June 2017. It is the successor to Debian 8 "Jessie" and the predecessor to Debian 10 "Buster". The Debian 9 release is the result of over 2 years of development and testing by thousands of volunteers around the world.
Some of the main features of Debian 9 are improved security, addition of new software, improved manageability and performance optimization. Debian 9 includes the latest versions of many software packages, including Linux kernel version 4.9, GNOME 3.22, KDE Plasma 5.8, LibreOffice 5.2, Apache 2.4.25, PHP 7.0, MySQL 5.7, and many others.
This version was maintained by the Debian Project until 2020, after which it moved to "oldstable" status.