Anyone know if this site http://soundsnag.com a custom developed site or is there a script out there with all of these features that allow people to add their own free sounds?
Yes it looks that it's custom developed but this can also work if you use wordpress with buddypress and some extra plugins or simply you can use a youtube clone theme, it's almost the same thing but for videos, if you customize it a little you can make something similar with the site you asked about. Cheers, Zoomx
Looks like a reddit for sounds. Pretty cool. Whether or not it will take off, I don't know. It's probably a custom made script. You can ask them directly: http://soundsnag.com/play/contact
It is like developed using custom PHP script. It is use a script which is describe that site is a script in in its nsource.