Prepar3D Tweak Assistant (PTA) is the evolution of a once shareware program that was just released a couple of days ago.
The originator had become discouraged. Hosting and maintaining the program was taking up more and more of his time with VERY little return.
A new person, Matt Davies, thought that he could move it forward, and hopefully, make some money for his efforts. Long story short, he bought the rights to PTA (for substantially more than he had expected) and did a significant amount of work on improving it.
You can now buy the P3d V4 version for £14.99 (about $19USD).
The P3d V3 version is free, but you have to register on his site to download it. The V3 version looks to be similar to the V4 version.
Now, if you've heard nothing else about Prepar3d V4, you've heard that jumping in and trying to alter, or install, some files by hand can be disastrous, and require uninstalling P3d.
THIS program does it right. It doesn't keep you from making bad choices, but it does make the changes in the P3d files correctly.
What does it do, and is it worth it?
I'd have to say that it is certainly worth it, because I, as incompetent an "artist" as ever lived, can use it to get good results. Of course my first attempt was pretty horrible!
The important thing to know is that it makes backup copies of the files that it changes, so unless you go far outside of the normal settings range, you'll just be a click or two from restoring and starting again.
As to the "What does it do" part....
It would be better to let you see what it does - THE ULTIMATE TWEAKING TOOL - Prepar3D Tweaking Assistant (PTA) (YouTube video)
Or, if you can see this -
[youtube]http://www.youtube.com/watch?v=XHWt_KEzZVw[/youtube]
As easy as it is to use, you really should read the instructions, just a little.