Interstellar has always had support for M of N multisig accounts in a user friendly way. The signers don't even need to be in the same continent.
Another important detail about the way multisig works in Interstellar is that we don't provide any additional signers ourselves. You manage all of the signers you need.
As soon as each signer logs into his Interstellar account, he/she receives a notification with all pending transactions that require his/her signature.
The signer is then given an opportunity to either sign or reject the transaction. If enough people sign the transaction, the signed transaction is submitted to the Stellar network. If enough people reject the transaction, the transaction is forever destroyed.
Recently, our multisig UI got a facelift. Here's a screenshot of how it looks now.
Your secret keys always remain on your device. Never sent anywhere. And each signer gets to see a preview of the transaction before signing.
Another interesting detail about the way multisig works in Stellar is that additional signers don't even need to be funded!
Multisig is a great way to keep your account safe against theft and loss.
You can for example use a 3 of 5 multisig account in a corporate environment so that 3 out of 5 partners have to sign to validate a transaction.
You could also for example set up a 2 of 3 multisig account for your personal account to keep your funds safe. One key on your desktop, the other key on your mobile phone and a last key on your tablet. That way, you'll need to sign on both your desktop and mobile phone for transactions to be valid. And if your phone gets stolen, you can always sign with your desktop and tablet, while waiting to get a new phone.