The evolution of the exchange-traded fund (ETF) brought innovative products to the fixed income marketplace. These don't just cater to buy-and-hold investors fixated on the long-term investment horizon. Ultra-short term bond funds appeal to investors looking to use the ETF wrapper to fulfill short-term cash obligations. It's what Morningstar's head of client solutions Ben Johnson referred to as "money market substitutes†in a recent episode of ETF Prime. In the same episode, Johnson picked the Vanguard 0-3 M ...