Robinhood's new feature, called Cash Management, takes a more traditional regulatory approach than its last foray into bank accounts.

The ETNs, which are set to start trading on Tuesday, will track gold and silver futures contracts.

So-called authorized participants, or APs, act as gatekeepers for every dollar that enters or exits an ETF.

“Investors are like hyperactive first graders playing musical chairs -- always trying to out-anticipate the other as to when the music will stop.”

Online B/D TradeStation Securities and online brokerage Ally Invest are offering commission-free trading.

Charles Schwab Investment Management will offer 3 new bond ETFs as of Oct. 10.