Cosmian KMS (https://docs.cosmian.com/key_management_system/) is an open-source key management system that delivers exceptional performance by enabling massive client-side encryption on the fly.
Cosmian KMS offers a KMIP 2.1 interface, simple horizontal and vertical scaling, and ready-made connectors for various existing applications.
The KMS is available in multiple packages and multiple operating systems. It has also been designed to run confidentially in the cloud by leveraging Cosmian VM, a hardened OS that runs on confidential computing machines that use encrypted disk and memory. Pre-packaged cloud KMS are available on the major cloud providers' marketplaces (https://cosmian.com/data-protection-suite/cosmian-kms/)