We used this to build account recovery modules for wallets, which is live for Gnosis Safes at prove.email/recovery , which allows anyone to add an email address as a decentralized guardian for their wallets. We discussed this at ZK Summit: https://www.youtube.com/watch?v=rZTNzvLXB14 . 

We also built email wallet (demo: https://emailwallet.org, docs: http://docs.emailwallet.org) as an open standard and protocol that anyone can plug into -- it allows you to use your email as a wallet signer, allowing much easier onboarding onto Ethereum. In addition, plaintext emails serve as a one-click replacement for hot wallets, for signing and sending transactions. It also lets anyone send any NFT directly to any email address. We also released 2 factor authentication via email signers on Safes using emailwallet.org (https://prove.email/blog/2fa) and general email-login based authentication modules via email wallet (https://zkemail.gitbook.io/zk-email/login-with-zk-email-oauth-api).