> Going even farther than that direction, there's muni bonds, funds, or money markets. At which point you're probably back to Vanguard for the best rates. (But again, not the same exact characteristics as a savings account)

Yeah, very different product. Muni bonds are riskier than treasuries and much longer term than money market funds / treasury bills. E.g., VWSTX ("ultra short term muni") has an average maturity of over a year and 45% of portfolio is worse than AA. Vs VMFXX (money market) with an average maturity of 11 days and the entire portfolio is backed by the US government, which is essentially as good as it gets.