Siliconera has uncovered a Nintendo trademark filing in Europe for "WiiRelax".
The site speculates that the title might apply to software for the Wii Vitality Sensor, the pulse-measuring peripheral that president Satoru Iwata revealed at Nintendo's E3 press conference last summer. Seems a reasonable supposition.
An Italian developer called Pub Company also announced a product called Wii Relax back in April this year, but no mention has been made of this recently and its website has disappeared.
According to Nintendo of America's president Reggie Fils-Aime, we'll find out more about the Vitality Sensor at E3 2010.