* And just like the stock market, there's a market for these: banks with excess deposits offer repos at a variety of interest rates, and banks with excess loans take the best available interest rate, and eventually the market converges on a particular market-clearing rate (the "Fed Funds Rate").*

With the small and pedantic correction that the Fed Funds rate doesn't measure repos, because it measures unsecured lending, and repos are secured. It's the Secured Overnight Financing Rate that measures repos.

But yes, when the Fed wants to push the Fed Funds rate around, it does it by getting involved in repos - because if banks can borrow from the Fed at 2.4% through a repo, they aren't going to borrow from other banks at 2.41%. You'd think there would be a bit of a spread between the rates, because banks don't have to put up collateral for unsecured borrowing, but in practice there doesn't seem to be.