> if anyone accesses app developed by you, they can use it freely without any license.
This is simply incorrect on every level, starting with the fact that (in the US, anyway), you can't place your works in the public domain even if you wanted to.
That's not true in at least one case: if you work for the US federal government, all of your works are automatically in the public domain. Of course, they may also be barred from disclosure for other reasons.
You're correct, that's the one exception. Although you could argue that it's not really an exception -- it's that when you're producing IP in the course of your employment, your employer owns the copyright. And if you work for the federal government, your employer is the American people, so in a real sense we collectively hold the copyright. Which is the same as being in the public domain.
This is simply incorrect on every level, starting with the fact that (in the US, anyway), you can't place your works in the public domain even if you wanted to.