"Akira Toriyama is rumored to be making a new Dragon Ball series alongside mangaka Naho Ooishi, the creator of the 2008 Dragon Ball Z special "Yo! Son Goku and Friends Return", called Dragon Ball Hoshi. Ooishi will be making a manga that continues the Z manga past the Buu Saga. It will have a newly designed Super Saiyan 4, and even a Super Saiyan 5. Akira Toriyama will be assisting her and backing off. The events in japan (earthquake, tsunami) slowed this down now Toriyama is taking care of that. It's rumored to be out later this year or early 2012."
What most people are calling "Dragon Ball Hoshi" is actually Dragon Ball Heroes, a Japanese arcade/card game, or Ultimate Tenkaichi. The Japanese word "Hoshi" means "Star" or "Wish/Wanted".
Dragon Ball Hoshi is just a rumor and there is currently no proof of it's existence.
Dragon Ball Heroes Official Site