This week Guggenheim launched the CurrencyShares Singapore Dollar ETF under the symbol [[FXSG]]. Guggenheim bought Rydex at some point and of course Rydex launched the first currency ETFs. Many years ago I asked a Rydex exec, his name might have been Steve Sachs, about launching this fund and he said there were obstacles to Singapore but apparently they worked them out.
Singapore is generally a very stable currency and is a benchmark of sorts in Asia, or maybe better thought of as a relative safe haven. The chart shows the pretty slow and steady decline of the US dollar compared to the Singapore dollar except for the worst of the financial crisis. The hit to SGD during the crisis though was nothing like the drop in the iShares Singapore ETF (EWS - News), which offers equity exposure to Singapore - EWS was down 60% at its worst.
Over the years we've done a couple of things with currency ETFs although it has been a few years since we last used one. I imagine we'll use currencies at some point again but I'm not sure when.