Is there any legal constraint saying that a commercial software must quote the open source libraries and public domain libraries regardless of the open source license type?
For example, let's say I develop a web application based on java servlet and I include (and use without modifications) a library licensed under Apache License 2.0.
Then I will sell my .war file that includes it.
Do I have to include a text file saying I am using it? What would/could happen if I don't?