There is none I can recommend, because no multi-currency web wallet supports multisignature. Dont use online wallets that do not support multisignature wallets.
If you understand that, to answer your question, there is only one wallet I know of which supports darkcoin and some altcoins, its https://holytransaction.com/ - but I can not recommend it, as your funds are not secured with modern state-of-the-art multisignature security features, like bitgo.com or similar sites offer.
Edit: Do not use web wallets without multisignature.
BetCoin, a native exchange system supports multiple cryptocurrencies in a single wallet. Currently, BetCoin supports BTC, ETH, Litecoin, Ripple and Dogecoin. More cryptocurrencies will be supported in the future. The multi cryptocurrency wallet feature distinguishes BetCoin from the rest of the exchanges.