Can you install GNU/Linux applications onto this OS or is it impossible? If it is impossible, then would compatibility for GNU/Linux be supported?
This is impossible, Haiku and Linux are different systems. Applications are not compatible in binary (executable) format. Haiku is different like different are Windows and Linux, or MacOS and Windows.
However, a number of Linux/UNIX/BSD applications and libraries have been already ported to Haiku. They are installable on recent Haiku nightly images.
The best answer to this is no… and yes. No, you cannot run binaries made to run on Gnu/Linux. If you tried to get SpaceFM, for example, to run as it is, it will not work. But the other answer is yes, in that you can run a few libraries and applications that have been ported to Haiku like LibreOffice 6, Qupzilla, Tux Command, SuperTux, etc. which are available as various packages or in the repos.
Anyway, hope this helps.
There has to be something like wine for Haiku that allows GNU/Linux applications to run? Otherwise how can people use this OS when GNU/Linux is far more popular?
Who ported these applications?
Here is the story behind libreoffice. Hope you find what you are searching for n-n
Short answer: various members of the community. The port of LibreOffice 6 is new and for x64 only; would have mentioned Krita and KolourPaint, but they crash last time I tried launching them. The other two should be in a repo (the kids’ game and Qupzilla). As for SuperTux, it ran on BeOS before the Depot.
Krita 4.1.0 and KolourPaint 18.07.80 both work for me (on x64).