You get to keep only enough to maintain a very modest lifestyle in a low-cost-of-living area, the rest of it has to go towards improving the world in some way.
Edit: Given the previous rules that you must maintain a very modest lifestyle in a low-cost-of-living area, would you rather choose to opt out and not have the money at all?
I would set up a program where the teachers in Philadelphia public schools would have their school supplies highly subsidized by myself.
The local food banks would receive five figure donations directly from myself.
I would look into water retention and distribution in drought stricken parts of Mexico. If I could help I would leverage my money effectively to make sure humans have access to safe drinking water in the region. If acting directly would cause harm I would fund researchers until an appropriate solution could be found.
Create an app that teaches the indigenous languages of the Americas while hiring native speakers for accuracy.
Edit:
I like your very targeted responses!
With money in the billions, I agree that I couldn’t not help fellow humans first.
Your proposals also have some fairly immediate benefits to a number of different groups of underserved people.
And then you even came back in the end to include some of the critters as well!
I like your style.
If I got billions of dollars at this point how could I not throw a little at the owls. I would feel guilty everyday I open my subscriptions.
It is a nice feeling to see it means something to all of you!