The LevelUp API enables you to integrate LevelUp's seamless mobile payment + loyalty solution into your application. Initially our focus is mainly to expose this API to POS software providers and integrators so they can integrate LevelUp right into the POS. Of course there are tons of other use-cases also. Let us know a bit about who you are and what you'd like to do and we'll get you access to our dev tools and credentials to start hitting the API.
You can learn more about the specific API calls exposed here: http://support.thelevelup.com/categories/20030813-developer-overview
And finally, please be patient with us. The LevelUp API is definitely in beta and we're going to be iterating and working to improve it rapidly. We're excited to hear your feedback.