I might start up my own non-profit. Or I might start my own for-profit business. Normally that would be financially risky but...hey...billionaire. Then again if I'd already started my own business and had it be wildly successful, which is why I'm a billionaire in the first place, I admit I wouldn't be as motivated to try it again. Might just stash 50 million somewhere and give the rest away. 1% interest (after inflation) would be $500k/year.