Hi,
As you may or may not know, a short while ago, I created my very own sound scheme for Windows. I still don't have an installer or anything else that will allow this scheme to be automatically applied yet. However, I have released the individual sounds for the scheme as a zip file.
These are all original sounds, composed by me. This is my first attempt at making something like this.
The scheme is called Pliocene (ply-oh-seen), and the zip file containing the sounds can be found here: https://www.houseoffireseed.ml/soundhouse/pliocene.zip

Which version of Windows is this for?

It can, in theory, be used on any version of Windows that supports sound schemes. However, I haven't done any of the Windows 8 + sounds like alarms and NFC proximity stuff, since nobody really uses those sounds besides, maybe, people who still think Windows Phone is cool and those with specialist devices where NFC is a thing.

Great for a start, I'd just personaly add a bit of reverb to the sounds to smooth the endings.