Since Gist was bought by RIM a mere two months ago, it was inevitable that they would be making an app. Of course, these things can take time but it looks like there will be an app coming out soon. In the meantime you can sign up for the app and Gist will let you know when it is available.
Sign up is here. It is a survey, so you are going to be asked some questions, which will help them to improve the product.