Why is it so difficult to program this feature and design something with two panels if the software has supposedly ADVANCED? Yes, because it hasn't! they complicated but not better at designing things we can use easily to do something well.
It's not difficult. It's been done a thousand times over.
You're just not willing to do much research. This sounds a lot like notebook/mid-mapping/brainstorming software, and there are SO MANY options, quite a few of which would be similar to Idea Knot and probably many, many more that are BETTER, but not doing the research and the attitude of "I don't want to learn something else" is stopping you guys from finding a solution.
That said, there is another option or two -- since the OP needs to be able to open his old files.
The first is to buy/download the PC version of Idea Knot, which is apparently still being developed.
Idea Knot
This may be able to read his old files, and of course Macs can run Windows software with the help of a virtualizer like Crossover, VirtualBox, Parallels, etc. You'll want to check with the developer about the compatibility of the files, of course, and while you're at it check with them about the alleged "Pro" version of Idea Knot they say they are working on (don't hold your breath, after nine years!).
Another option would be to pick up a cheap old MacBook that's already running 10.6.8, put your old copy of Idea Knot on it, and use that as your "Idea Knot" machine.
But really the long-term solution is to convert the files from Idea Knot into some standard format, and import them into Evernote or Circus Ponies Notebook or TopNotes or DevonThink or YoJimbo or Together any one of (literally) a thousand more notes/ideas/mindmap apps that a basic search on MacUpdate.com or the Mac App Store would probably yield. I mostly use the built-in app "Notes" for this, since it syncs with my iOS devices and vice-versa -- a feature I consider vital that Idea Knot never even dreamed of.