Vaultoro
It is somewhat unusual, as it offers trading in bitcoin for real, physical gold and vice versa. The minimum amount of gold that can be traded is 0.001 Gram.
According to Vaultoro, clients can also trade directly with other members and without a middleman. The client sets the price and can save expensive brokerage costs.
As for customer verification, Vaultoro requires its clients to verify their accounts before starting to trade. For the purpose, a client needs to upload a copy of a driver's licence or passport as well as a photo of a utility bill no longer than 3 months old.
Like most crypto exchanges, Vaultoro offers its own web-based platform, which has some basic features such as price chart, volume chart, as well as an order book. Clients can place market, instant or limit orders, view their trading history and deposit and withdraw assets.