Most regulated forex brokers today offer at least a few metals for trading in the form of CFDs. Most of often, these metals are the precious metals gold and silver, but some brokers also offer other metals like platinum, palladium, copper, and aluminum.
Out of all the metals that are offered by regulated forex brokers around the world, gold is by far the most traded one. This has to do with the monetary properties of gold, and its traditional use as a hedge against inflation in fiat currencies. Silver has for periods of time also played a similar role, but is today considered more of an industrial metal than gold is.