Server scripting 

1. PHP

UI/UX

1. CSS 1, CSS 2, CSS 3 (pre-processors: SASS, SCSS)

Databases

1. PHPmyAdmin
2. MySQL

OS

1. SSH: Linux distro’s (Ubuntu, CentOS 6, CentOS 7)
2. MacOS
3. Windows

Software optimalisation

1. PHP 5 / PHP 7
2. MariaDB / Percona