Ubuntu Server download:
https://ubuntu.com/download/server

Snort Website:
https://snort.org/

Windows Server Evaluation Copies:
https://www.microsoft.com/en-us/evalcenter/evaluate-windows-server-2019

Metasploitable2:
https://metasploit.help.rapid7.com/docs/metasploitable-2

Kali Linux:
https://www.kali.org/downloads/

Nmap (if not already install / not using Kali Linux)
https://nmap.org/download.html