Exchange-traded funds are designed to be building blocks that are easy to put together. You can find stock-focused ETFs of all kinds, which you can mix and match to customize your own particular exposure to stocks. You can then pepper in ETFs containing other types of investments, including bonds, commodities, cryptocurrencies, or just about any asset class you can think of.Some investors, though, would prefer to have a single ETF that would handle all of their investment needs for them. This led the fund m ...