Peerunity is a client developed by the Peercoin community as reponse to low activity with development of official Peercoin client by Sunny King. It includes features beyond the core protocol wallet, such as one-click minting, coin control, multisig control and a minting tab. Future releases are scheduled to contain a redesigned theme, as well as possible Peershares integration.
In a traditional Peercoin wallet, you have Peercoin addresses, where each address has one associated private key that grants the keyholder full control over the funds. With multisignature addresses, you can have a Peercoin address with three associated private keys, such that you need any two of them to spend the funds. Theoretically, you can have one-of-three, five-of-five, or six-of-eleven addresses too; it just happens that two-of-three is the most useful combination.
Multisignature addresses are used in practice for increased security or escrows. When Sunny King wants to send $20 to Satoshi in exchange for brand new Britney Spears CD, Sunny King first picks a mutually trusted arbitrator, whom we’ll call Bob, and sends the $20 to a multisig between Sunny King, Bob and Satoshi. Satoshi sees that the payment was made, and confirms the order and ships the product. When Sunny King receives the product, Sunny King finalizes the transaction by creating a transaction sending the $20 from the multisig to Satoshi, signing it, and passing it to Satoshi. Satoshi then signs the transaction, and publishes it with the required two signatures. Alternatively, Satoshi might choose not to send the product, in which case he creates and signs a refund transaction sending $20 to Sunny King, and sends it to Sunny King so that Sunny King can sign and publish it. Now, what happens if Satoshi claims to have sent the product and Sunny King refuses to release the funds? Then, either Sunny King or Satoshi contact Bob, and Bob decides whether Sunny King or Satoshi has the better case. Whichever party Bob decides in favour of, he produces a transaction sending $1 to himself and $19 to them (or some other percentage fee), and sends it to that party to provide the second signature and publish in order to receive the funds.
Please note that Peercoins located in multisig address will not be seen in any of participants wallets as wallet will only show the funds it can control.
To learn how to use Multisig with Peerunity, visit tutorial: Using multisig with Peerunity