Keyper is described as 'Open Source SSH Key and Certificate-Based Authentication Manager that acts as an SSH Certificate Authority (CA), standardizes and centralizes the storage of SSH public keys and SSH Certificates for all Linux users in your organization' and is an app. There are three alternatives to Keyper for Linux, Flathub, SaaS, Flatpak and Windows. The best Keyper alternative is Key Manager Plus. It's not free, so if you're looking for a free alternative, you could try KeySmith SSH.
ManageEngine Key Manager Plus is a web-based key management solution that helps you consolidate, control, manage, monitor, and audit the entire life cycle of SSH (Secure Shell) keys and SSL (Secure Sockets Layer) certificates.
KeySmith is a modern GTK4/Libadwaita application that provides a user-friendly graphical interface for SSH key management tasks. It simplifies the process of generating, managing, and deploying SSH keys through an intuitive GUI while maintaining security best practices.
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