There was a time that Windows was shipped with the "Terminal" application that allowed users to connect to modems and other serial devices. Now that its no longer available, putty is the defacto replacement. It is an excellent serial communications application and also handles all text based linux and bsd communications via ssh.
This is a go to tool for any technical person that must support serial devices and linux freebsd or other non-windows computers. Its stable, reliable and quickly installed whenever necessary. For testing whether a server has working and open ports, PuTTy is an essential tool. It allows a connection to be made to any port to see if the port can be opened and then enables simple handshaking to take place to confirm the appropriate service is up and responding on that port.
You can tell a lot about a technician by seeing if PuTTy is installed on their computer. Without PuTTy, they will not have the skills or experience to manage Linux, FreeBSD and other critical devices.
PuTTY/SSH Intro Tutorialhttps://www.youtube.com/watch?v=9CZphjhQxIQ
The official website for this software utility can be found at: http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html