OpenZeppelin Relay

OpenZeppelin created its Defender Relay service to allow users to send transactions via a regular HTTP API. Defender Relay provides a gasless meta-transaction relay that ensures a seamless and cost-efficient experience. For developers, there is no need to monitor transactions or use a backend script to secure private keys because the protocol takes care of everything from resubmissions to private key secure storage to the signing of transactions.

Biconomy Core

Biconomy (BICO) is a multi-chain, plug-and-play relayer protocol that manages transactions, gas payments and bridges for Web 3.0 applications. Users can leverage smart contract wallets and build custom transaction journeys within a single platform. For developers, Biconomy offers developers powerful and easy-to-use SDKs/APIs which enable them to build decentralized apps (DApps) with a customized transaction journey