It seems you misunderstood me. To clarify, I opened this thread because in real life it is important to use at least 2 different solvers. Of course I tried out CalculiX with FC and it works fine. Nevertheless, using the same mesh in Z88 gives me other Eigenfrequencies than CalculiX and this is what I expected. Therefore it would be very valuable for real life application if FC would offer to perform simulation with different solvers.
It might be that Z88 is not bleeding edge or doesn't have much user activity, but it seems that one can rely on its results. Therefore Z88 support should stay and it should be possible to use all analysis modes of Z88.
Concerning Z88 Aurion, I tried it of course already and that V1 of this solver did not have any output was kind of ridiculous. V2 offers now at least STL export. It is clear that this is not sufficient for integration with FC.
It seems to me that Z88 works together with companies and therefore they don't offer that many possibilities. This would also explain the low activity on the Z88 forum because as employee you are normally not allowed to post in forums (on what project would you book this time etc.).