All of these comparisons are misleading and wrong

Keyclone is probably considered the "baseline" around here; a lot of people still use it and some people even consider it easy to use. It is kind of simplistic.

******** is like a Keyclone clone that's missing various features (e.g. round-robin, support for multiple PCs) and has a different UI. It's just a cash cow for a web site its owner is trying to promote, and the software doesn't get updates (neither does Keyclone these days, but that's beside the point). When you search on google, you will see a lot of his sites pointing back to his main site, because he doesn't want you to find his competitors -- if you're well-informed you'll probably not decide to pay for his product.

HotkeyNet revolves around a custom programming language that lets you build your multiboxing setup within the confines of the language. Similar, in a way, to AutoHotkey. It was originally built for Dark Age of Camelot, but DAOC changed their rules earlier this year to prohibit multiboxing software (you can also read my recent rant about this on this ISBoxer.com thread). If it were coupled with an easy to use GUI, there would be no particular reason to purchase Keyclone or ******** over a free HotkeyNet because it can perform every single function they do, if not more. Just the fact that it HAS such a configurable language means you can do things in HKN that you can't do in KC or the other.

ISBoxer is built on Inner Space, which makes it different from all of the above. Inner Space is kind of like a window manager and application virtualizer for Windows, except that it operates only on specific application windows (DirectX games launched by Inner Space). That basically means that Inner Space can do things like redirect files to another location (e.g. have WoW load a different file in place of Config.WTF for different configuration in each window), or "lie" to the game about the appearance or behavior of the game window (thus the ability to make window swapping truly instant, or to allow each game window to think it's the foreground in order to allow broadcasting -- necessary for multiboxing games like EQ1, EQ2, DDO and LOTRO on one PC). These are normal things for the operating system to be doing, and if you've got Windows Vista or later you may already be somewhat familiar with this kind of idea -- for example, Windows has a virtual file store that if the game is installed under Program Files and is not running as Administrator, will redirect data file storage to that location. So Inner Space does these things in an agnostic fashion, and in pretty much the same way Windows applies such "fixes" (in other words, there are no WoW hacks involved). Inner Space also has in-game overlay features, similar to those in X-Fire, Steam, etc (thus the ability to show each window's actual cursor while mouse repeating is on, clickable buttons in the game, semi-visible regions that automatically broadcast the mouse to other windows, etc). ISBoxer helps you configure all of these things by generating an Inner Space setup. These are just the things that you CANT get with other multiboxing software currently available. Not because the other available software is particularly "bad" -- they perform key broadcasting functionality and in many cases mouse broadcasting functionality just fine, they have basic window layout functionality, etc -- but because the simple design doesn't provide for it.

ISBoxer also has a lot of ease of use features built into the configuration GUI, wizards and the sort, and generates a WoW Addon with macros you configure through ISBoxer. And, like HKN, there is a language underneath that if you really wanted to, you can pretty much make any changes to it that you want within the confines of the language.

I'm trying to be as unbiased as I can, obviously I'm the author of Inner Space and ISBoxer.

So here's my analogy:
* Keyclone is like a Model T, people might consider it "the original" and some people still drive it (Although people drive Keyclone a lot more than they would be driving their antique Model T )
* ******** is like if a Chinese factory made a Model T knockoff and both cheaped out on the materials, left some parts out, and added some random crap that you aren't sure why they thought it would be a good idea to put in your car. It still "works", the original vendor is kind of ticked about it and it might be illegal to import (to dual-boxing.com)
* HotkeyNet is like getting a free kit to assemble your own car. Make it a Ferrari a la Zynga, whatever. I'd suggest this Lamborghini instead: http://jalopnik.com/5065896/hand+mad...s-light-of-day.
* ISBoxer is like a souped-up DeLorean DMC-12. It does everything other cars could possibly do, but when you get it up to 88 miles per hour the flux capacitor kicks in and you discover that it is truly unlike other available cars.