I recently dug my old Kindle 3 from 2010 out of the drawer and started playing around with it. I looked online to see if it had any capabilities beyond reading books and I was surprised to see that there is an active community of people that are rooting these devices. I rooted mine and did a few simple things like changing the sleep screen pictures and installed a better audio player. I then found a post that linked me to a VNC viewer for kindle and I immediately tried it out. I set the host client up to my pc, lowered the resolution to that of my kindle (800x600) and connected wirelessly through LAN. This post is the first thing I've done with it. This entire post (except the links up ahead) has been typed remotely on my kindle 3 wireless.
Off the Kindle
Here is the link to the "Jailbreak" https://www.mobileread.com/forums/showthread.php?t=88004
This is the link to the VNC viewer for the kindle https://www.mobileread.com/forums/showthread.php?t=151984 The link the OP provides is no longer active, but someone a few posts down has put the direct download link in the thread.
MobileRead is the main source for all these kindle hacks if you are interested and there is even an entire page dedicated to software for the Kindle 3 here https://www.mobileread.com/forums/showthread.php?t=128704
You can get a lightly used kindle 3 on Amazon for $30