UltraStar

Quote from Wikipedia:
"UltraStar is a clone of SingStar, a music video game. Ultrastar lets one or several players score points by singing along to a song or music video and match the pitch of the original song well. Ultrastar displays lyrics as well as the correct notes similar to a piano roll. On top of the correct notes Ultrastar displays the pitch recorded from the players."
For the full description, click here.

To download the Mac (intel) version, click here.

For songs to download, click here.

kJams can load and play the textual lyric and audio portions of UltraStar (SingStar) songs, and Producer can turn them into CD+G streams suitable for burning to disc.