Like the idea of having karaoke parties at home? If that sounds like you, dextrus has the answer:
Earlier, we tried getting a sort of Karaoke system working on the Pi. The idea was to use the built-in alsa sound system that comes with Raspbian to capture the microphone and pass it through to the speakers while simultaneously running some sort of Karaoke program (our plan was to use something on XBMC). Sadly, the alsa sound system was a bit broken such that if you tried to play two sounds at the same time, when the first sound finished the entire sound system would crash and you would have to reboot the Pi. This spelled the end of our Karaoke plans.
HOWEVER! There has since been an update of the sound system. It’s not perfect and it still crashes, but it doesn’t crash THE WHOLE SYSTEM, It seems to just corrupt the process that you were running. Further investigation lead to the discovery of a lightweight youtube player (whitey, using OMXPLAYER) and a way to run alsaloop to capture the microphone AT THE SAME TIME! Effectively, a proper Karaoke system!
Head over to www.pi-fun.com to see how to set up your own pi powered karaoke system!