From Breakthru Software:
With Matrix Mic & Player, you can use any computer connected microphone to broadcast announcements to one or to multiple sets of computer connected speakers simultaneously. The Player lets you build, play and save Playlists of audio files (music or voice recorded announcements) from your hard drive (or other drive). You could also play music feeds from a Line-In or USB connected device such as an MP3 Player.
Examples of typical venues include theaters, shopping malls, retail stores, office buildings, sports venues, schools, haunted house walk throughs and other public venues. Hobbyists can use it at home as an intercom to basement or garage.