This was done as a method of learning Flex, the new wonderful Framework for Flash.
This application selects and plays tracks from the audio portal displaying information on the song and author. You can select tracks from a channel listing, each channel is currently based on the type of music, and every day the listing is updated with the top 50 songs of the listing. No bad music! :)
Songs are streamed and over 1500 songs are available for nearly every channel, so you can enjoy the top music of Newgrounds any time.
If you'd like a specific feature, or want something changed with NG-Radio for later version, feel free to let me know. An AIR version of NG-Radio will be released later, which will let you use a low memory (no browser like IE memory leaking all over the place, just a nice clean AIR app) that will plugin to the System Tray and let you hide and show any time you like music. I will update this when the AIR version is complete, and you can also find news about it from the small news box shown in NG-Radio.
I realize that NGAP has many of the same functions as NG-Radio, but they were both developed with different ideals and features. If you like NGAP more, stick with it. :)