So Marketo does have an app, but it is pretty limited. Usually you have to pre-load it with the people that are registered to attend and then you can check them in. I think there is way to add people that stop by your booth, but you have to mannually type in their info.
One other solution, is to use a third party app that integrates with Marketo. One example of this is called atEvent. You can find them in the launchpoint ecosystem here: http://launchpoint.marketo.com/atevent/843-atevent
Their system is pretty easy to set up with Marketo. It has more capabilities than the Marketo app. One of the biggest advanteges this solutino has, is it can scan people's cards/info in automatically, like a badge scanner.
It is about 6 months old and they are still working on making it better. There are things that can be improved on it, but it is a decent solution.