Telnet is an older, text-based protocol originally used for sending commands to remote computers. It was one of the first methods of communication on the internet. It's not particularly common, but there are some telnet servers still available. Try telneting to towel.blinkenlights.nl (or with this client).
This is a JavaSSH client wrapped inside a simple program that allows you to click on a telnet:// link and automatically use this client. All you need to do is This is useful because many modern web browsers have no telnet client, and while telnet isn't particularly common anymore, it does come up on occasion.