We have that, that's called a (federal) money market mutual fund. Edit: sorry, you said the Fed, which MMMFs don't put money in. But they buy short-term Treasu

We have that, that's called a (federal) money market mutual fund. Edit: sorry, you said the Fed, which MMMFs don't put money in. But they buy short-term Treasurys at comparable or better yields, which is ultimately what you want, modulo the risk of US government default, which is minimal.