I didn't realize people have been implementing multisig. For example,
GreenAddress.it has 2of3 accounts, and so does Coinbase, which they call
Vault.
GreenAddress and Coinbase Vault are both intended for individuals, or for individual employees (the multisig for these wallets is intended to keep individuals safer from malware, it's not intended to prevent embezzlement).
There
is multisig software designed for companies or groups of individuals though. You may want to look at
Armory (lockboxes),
mSIGNA, or perhaps the recently released
Electrum 2.