Yes there's a way to get ISBoxer for free, but you'll need Windows 7 and Java 7.
It's a very old version so you won't have most features that are available with the official ISBoxer, and your performances gonna be reduced a lot.
(For example I used both ISBoxer 1.11 cracked and the Official one, with the cracked version I can run 12 characters maximum else it's starting to be laggy even if I'm not in a city, and with the Official version I can run 20 without lagging, just some FPS drops in BGs or mass PVP).
You should buy the 3 months subscription to try ISBoxer, you'll see it's very powerful and there are tutorials on YouTube. ISBoxer is way better than Octopus, Quinbox and even HKN.
Anyway, if you want to get it free, send me a PM. I can give you ISBoxer and the a working java installer.