Probably the simplest browser window. Lists the loaded packages.

You can click Play to play the music and Stop to stop playing the music.

Menu options

• File->Open
  open a music package
• File->Save
  save the package as a new name
• File->Export
• exports the file to a .S3M file. Unfortunately it names it .WAV. Rename the file with a .S3M extension and winamp will then play it.
• Files->Import
  I don't know that much about music, but I'm guessing you have to create a S3M file, rename it as .WAV and then import it into UnrealEd.
• Edit->Play
• Edit->Stop
  Guess what, play the music and stop the music!
• View->Docked
  Changes the docking status of the browser