Exchange-traded funds promise low-cost exposure to a wide range of asset classes and strategies previously unavailable to small investors. Their appeal now extends to just about every type of investor, with global ETF assets reaching US$1trn at the end of last year, according to a new report from fund manager BlackRock.

The report counts nearly 2,000 different ETFs at year-end, many of which track benchmarks far more exotic than the simple equity indexes that marked the industry’s early years. Some of the more “innovative” ETFs have courted controversy recently amid allegations that they fail to explain their relationships with purported benchmarks.

Twenty years ago, it is unlikely that the ETF industry’s founders ever imagined a double-inverse bank index fund, to say nothing of such a vehicle providing some people’s livelihoods.