Brilliant.org aims to bring a challenging intellectual, online environment to everyone with high aptitude and interest in math and physics.  It offers weekly olympiad-style problem sets that are “rigorous, competitive, whimsical, and edifying” and scaled by level of difficulty.  You can join online to find your level and then work on new weekly problems, review practice problems, and discuss solutions.  Points you earn can be exchanged for e-books and a Brilliant T-shirt.  In a recent TEDx talk, Brilliant’s CEO explains how Brilliant aims to scout worldwide for intellectual talent in STEM.