(NOTE: This is a necropost, but it's important. I mostly post this in the hopes that this triggers notifications.)
Sadly, OpenSFX is not "open" (read: libre), because the CC Sampling Plus 1.0 license has some nasty restrictions in it. Creative Commons has retired this license a very long time ago for this exact reason. The FOSS community generally considers this license to be non-free, and for good reason: It forbids use in almost all forms of "advertisements" or "promotion", which is very broad. There are many other problems as well, you can read up on it here
Also, a few sounds were based on sounds with other problematic licenses (CC BY-NC, or no license at all).
Two days ago I have begun the process in redoing the sounds which are based on clear non-free source sounds, i.e. sounds under clear non-free licenses. Those were the obvious candidates that need replacement no matter what. I already tried to reach out to a few of the original authors for a possible license change, and I managed to convince a few!
But not all.
However, many sounds in OpenSFX are actually based on libre sounds, which is good. But they are still under CC Sampling Plus 1.0 because that's the license the sound editors
who worked on OpenSFX chose. That's a very unfortunate choice of license right there. I write this post here to kindly ask all of the original sound editors who edited the sounds of Freesound for OpenSFX to give their permission to relicense their sound edits to an actually libre license for the OpenSFX project. I also posted on GitHub: https://github.com/OpenTTD/OpenSFX/issues/6
(I do not yet suggest a new OpenSFX license yet, but it definitely should be a free culture or FOSS license, like for the rest of OpenTTD.)
This will greatly simplify the process of creating an OpenSFX that is actually "open" (read: libre).
If you are one of the original editors, please reply if you wish to give permission. Please also reply if you explicitly do NOT want to give permission (for whatever reason), this helps with planning ahead.
Please also refer to this thread for the quest to rid OpenSFX of CC Sampling Plus: viewtopic.php?f=29&t=85815