I like Cashu. It has a bit of the wild west feeling to it. I like FROST. It means you can do multisig without ever assembling a whole key in one place, and when you sign, multisig signatures look the same as single sig signatures.

Here's somebody putting these two together:

Collaborative threshold ecash, built on the Cashu Development Kit (CDK).

This is a fork of CDK that adds FROST threshold signing coordinated over Nostr, allowing a group of participants to collectively control Cashu ecash tokens.

Now, I do wonder a bit if these two things need to go together. After all, Cashu is a situation where you are fully trusting the mint not to rug you, so adding multisig security to that doesn't seem necessary...

But perhaps with automated bank runs (#404372) and proof of liabilities schemes (#1452462) it will be more reasonable to keep a balance on a mint.

Here's how the FrostyCashu process works:

Standard Cashu tokens are bearer assets: anyone with the secret can spend them. Frosty Cashu introduces collaborative custody using FROST (Flexible Round-Optimized Schnorr Threshold Signatures).

• Shared treasuries: A group manages a pool of ecash where no single member can spend unilaterally.
• Multi-device security: Require signatures from both your laptop and your phone before funds can move.
• Interactive governance: Force a human-in-the-loop approval process for every spend.

The final signature is a standard 64-byte BIP-340 Schnorr signature, indistinguishable from a single-signer signature. The mint never knows a threshold group was involved.