Where is the Matrix installer? I can't find it in the downloads, where it was. I have seen that the Matrix is no longer supported: ((

How can I install MAIW in Prepar3d v4?

Due to the termination of the Matrix project the Matrix download was deliberately removed from the Hangar.

I am not too sure on the specifics but I think I am right in that even if you have the program you either can't download the parts or soon won't be able to.
Removing the download was the easiest way to start the termination process.

Some discussions have started at looking as to whether the components of the download can be made available in any other way. No firm outcome has been agreed yet. If it is made available in another way then it will be purely a point in time offering with no updates and no support from the org.
It will require a manual installation process.

Once final analysis has been taken we will let people know the outcome.

Use Lorby's Addon Organiser to install stuff to P3D. It achieves much the same as Matrix did.