I have been researching texures and sounds lately and ended up buying most of them,
because of the legal mess that licenses invoke.
However I found a good thing that I just want to share here, for your information:
It is the
Creative Commons 0 license.
As far as I know, this is the only really free license that you can count on.
You need not pay or even give credit to something under the CC0 license,
and may use it for any purpose, including commercial.
Some other notes:
Also remember, that “royalty free” does not mean free. It means you buy it “one-off”
time and do not own percentages or monthly/yearly fees (called royalties). This is
a common misconception that many people, even professionals, fall to.
Also remember, that something provided without a license at all, does not mean it
is free or that you are allowed to use at all it in the first place. You may not “assume”
the license that fits you, just because there is no license.
Also remember , that there are other variations of CC licenses, that are almost free,
but need to give credit or other requirements. I am not very familiar with those, but
you might find interesting to read about them further.
So, bottom line = the only thing that is legally and totally free is under the CC0 license.
(as far as I know). The site freesound.org has a filter to show CC0 sounds and I use this often,
although I have found a nice bundle of 8000 game sounds for $54 and I will be using this