Nipper
SolarWinds - Firewall browser, Network configs and IP address Manager
Firewall Audit Tool
SSL Labs
Scan for threats
CVE Details
Nessus
Malwarebytes
Nmap
ZENMAP - Nmap Gui
WhatsUp Gold Starter
HPing
WireShark
Goscan → Open Source Interactive Network Scanner
Windows 10 got a built-in network sniffer