Its totally free but if you want to use the pro-version you'll have to pay some money. The advantage of using ntrconnect instead of vnc is, that you don't have to launch a seperate client program on your client PC. You'll just have to open your browser, press your username and password and then run an activex object.
VNC is also an alternative, but in my opinion not as easy-to-use as ntrconnect. Anyway, it was just a suggestion....