What theoretical advances have there been in relativity since Einstein?

(I originally asked this in r/AskScience)

So it seems that general relativity and quantum mechanics are currently our best working theories for describing the physical world, but from my knowledge of them it seems there has been a lot more theoretical development in the QM department in the last several decades, with QED, QCD, the standard model, etc. still being hammered out into the 70s and 80s. But off the top of my head (though I haven't taken any classes that go into the details of general relativity), I can't name any major developments from the relativistic side. Have there not been many, or have they just not gotten much attention? If there haven't been many, why?