"Sonic Rivals is a game in the Sonic series, developed by Backbone Entertainment exclusively for the PlayStation Portable. This is the first Sonic game to be developed by a Canadian company, and the first to be released on the PSP. It is also the first Sonic game to not be released in Japan. The game was also supervised by members of Sega Studio USA including Takashi Iizuka.
The gameplay featured in Sonic Rivals is mostly faithful to the classic Sonic games, but it features a 2.5 D style.
In the holiday of 2007, Sonic Rivals 2 was released for PSP, featuring Tails, Espio and Rouge, 150 more collectible cards, and new play modes."
Source: Wikipedia, "Sonic_Rivals", available under the CC-BY-SA License.