Lucky Kat Studios, who have done some quite fun games including Combo Critters [Free], are working on a really cool beat 'em up called Beat Street. The catch is that it's a one-handed portrait game, and all actions can be done with one finger, tapping and swiping to attack enemies, dash, and pull off special attacks. Roll that beautiful beat footage:

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I actually got to see a prototype back at GDC, and thought it was a really cool idea. Even in a very short development time, the core of the game felt like it could be a potential winner. Obviously there's a lot of work that needs to go into this one to take it from cool idea to cool game, but they have a big step out of the way. Beat Street is instantly one of my most anticipated mobile games, and you should check out the forum thread, where the developers are seeing if folks have any interest in beta testing this one at some point.