None.

Only-sometimes- a bus that runs in place of train as there are works on the rails. But in some of these countries they do not even offer that-in such a case you have to wait till works finished-or find other means.

Note that IF you mainly want to visit these countries, f.e. take the ferry from Ancona and then onward-forget a pass. Simply pay for your tickets when you go-it will be mostly bus and sometime train-local tickets are fairly cheap, sometimes still even lower as in IT.  

TREni in Bosnia and Serbije are very scarce, in fact there is currently NO intern. train at all to there (except to Monte Negro)