NSA Cyber Weapons Defense Tool is a free program which checks that your PC is protected from vulnerabilities relating to the leaked National Security Agency hacking tools. The most famous of these is EternalBlue, used by the WannaCry ransomware to infect hundreds of thousands of PCs, but there are many others.
The program is very simple. It looks at your installed Windows patches, checks to see if they include the releases Microsoft made for the NSA exploits, and warns you if any are missing.
If there's a problem, clicking the Fix button installs the missing updates.
You could do this already by running Windows Update on your own PC, of course. The sole advantage of NSA Cyber Weapons Defense Tool is that it has the patches included already, so works offline.