This has been split from this question..
So what are differences between two? Are there times where they can be interchangeable or can they only be used in certain situations?
I saw this about ことがある.
The question you linked to describes these usages in more detail, so I think I might leave those for now.
There are probably many other different usages too, but the two are generally quite different to each other as far as I know. I think as a (possibly broad generalization) that ものがある tends to be about feelings and tangible things and ことがある tends to be about abstract things, experiences and occurrences etc.