Roamy here. GRAIL stands for Gravity Recovery and Interior Laboratory. It launched this morning on a Delta II rocket from Cape Canaveral and is now on its way to the Moon. GRAIL is actually two spacecraft that will fly in tandem, measuring the gravity fields around the Moon. Scientists will use that data to learn more about how the Moon formed, how big the core is, and mass concentrations.
The tandem design was previously used with the Gravity Recovery and Climate Experiment (GRACE) spacecraft launched in 2002. The GRACE satellites gathered the same data for Earth, but with gravity changes related to ocean circulation, earthquakes, etc.
Updated with better launch video.
Updated again with satellite separation video. Everything nominal.