I wrote one a while ago in PHP, but haven't had the time to keep it up to date and secure.

It used a full node for blockchain information, accepted xpub's from admins/merchants/buyers, and generated multisig addresses. Private keys weren't stored or generated by the system, but eventually for usability, I allowed users to generate private keys using a passphrase in javascript. Convenience/Security trade off, but that's how it goes.

It lets users paste in signed raw transactions, or use the javascript thing to generate it in the browser if the user went that route. I'd love to revisit it, but it's a full featured site, not a module.