Currently I have hidden it on request by staff
(means you wont be able to download it)
The Brilliant app is now available on Windows Phone store. You can search Brilliant.org and the app by Megh Parikh is what you want(there are two apps but one is nothing but the mobile site)
Don't forget to rate it 5 star. Suggestions are welcome here.
This app was published without support from the Brilliant staff (I had amisunderstanding with them.) (I got free dev account due to my student status)