It's just Stir & Mix Radio, This addon may not be interesting.
Here the music in the radio has been changed, and this music is from the game Scratchin' Melodii, and this music is Stir & Mix (Vs. Jamtine), and Scratchin' Melodii creator is LJ Lephenstar. This is just an addon that changes the music in the radio. One problem with this addon is that it does not play endlessly (as far as I remember) and this addon took about more than 5 minutes, no more than 10 minutes
My first addon on Portal 1