A free telnet and SSH Client for Windows and Unix platforms.
And for me, it's not just free, but putty is ridiculously easy to use. It's fast and extremely lightweight download. As far as it goes, my putty has never experienced crashes/errors, making it a very likely tool for monitoring my network real time. It supports many protocol as well, so it's a very versatile tool to do task on many environments, be it Windows or Linux.
That screenshot was taken when I telnet my IPCOP box, using iftop command. No delay/lag experienced even when I do this online outside my network. All in all, this software is great to do remote task.