The Dreamcast Karaoke is probably the most useless Sega add-on. It serves no other purpose than to accompany the Sega Kara software, which is useless as well.
Back in the days you were able to download and sing thousands of songs, then in 2006 the servers were shut down for good.
Without the servers there are no songs – you can still connect microphones to the Dreamcast and listen to your voice with Sega Kara, change the volume and add effects, but that’s about it.