The only open-source wallet with cold storage and support for various signatures is Armony described on its website. This wallet is accessible for Bitcoin storage and solely for computer applications. It offers great level of security, because it never links to the Internet, like a cold wallet.
Briefly, Armony is a cold storage open source wallet that offers superior security for Bitcoin administration The wallet is just for PCs, the mobile application does not yet exist, and its website is not particularly appealing. Its UI is convenient for specialists in cryptocurrencies, but it may appear a bit hard to use for new investors.