Windows
Enabling the Windows telnet client
Launching the client
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Unless you're using Windows XP or older, your built-in telnet client is likely not enabled by default.
To enable it, first open the Control Panel by searching for "Control Panel" in the Start menu. Second, navigate to "Programs and Features" (or simply "Programs") and select "Turn Windows Features on or Off."
From there, check "Telnet Client" in the list, and let Windows apply the change.
Search for "cmd" in the Start menu, and open cmd.exe.
In the terminal winddow, type "telnet" and hit enter, to start the telnet client. In the client, type "o nethack.zacharymwyatt.com" and hit enter, to open a connection to the Nethack server.
You should see a screen like the one below.