Enterprising software developer James Laird was looking to stream music without AirPlay. Since an appropriate AirPort Express emulator did not exist, Laird reverse-engineered the Airport Express private key and published an open source AirPort Express emulator called ShairPort as a result.
What does that mean? A commenter on Hacker News spells it out clearly:
Previously you could do this:
iTunes -- stream to --> Apple Airport Express
3rd party software -- stream to --> Apple Airport Express
Now you can do this:
iTunes -- stream to --> 3rd party software/hardware
Laird has thrown the door open for software solutions. Now, you can stream music between Macs, to appropriately-configured consoles (like an Xbox), etc. ShairPort is built in Perl and C. Have fun, folks.