You need to install the Bethesda launcher to download them, but can use any mod pack to run it after (I like Quakespasm for Quake)
The amazing Trent Reznor music files are not under license but you can get 'em here and throw them into the file folder and turn on External Music and it works perfect.
https://steamcommunity.com/sharedfiles/filedetails/?id=119489135