I've come upon something called general Systems Theory but I don't know weather it is a scientifically mature field, if it has usefull applications already or if it is in an early stage of development. Has anybody read about this? Is it worthy of study? Or just another pseudo science or too-ambitious-to-be-done theory?

Yes and no.

 

There's always been a bit of woo in systems science, systems engineering, systems analysis, and that woo appears to have congealed in this general systems theory. From the wikipedia article on the subject: "As a transdisciplinary, interdisciplinary and multiperspectival domain, the area brings together principles and concepts from ontology, philosophy of science, ..." Come on. Multiperspectival? Concepts from ontology? Woo. That's the no part of my answer.

 

Now for the yes part of my answer.

 

For want of a nail the shoe was lost.

For want of a shoe the horse was lost.

For want of a horse the rider was lost.

For want of a rider the message was lost.

For want of a message the battle was lost.

For want of a battle the kingdom was lost.

And all for the want of a horseshoe nail.

That old proverb is a simple example of a failure modes and effects analysis, one of many techniques used in systems engineering to analyze, predict, and prevent problems. Systems engineering, system of systems engineering, systems science: They are very real, very useful, and they are not offshoots of this general systems theory.