chezmoi helps you manage your personal configuration files (dotfiles) across multiple machines. It is particularly helpful if you have spent time customizing the tools you use (e.g. shells, editors, and version control systems) and want to keep machines running different accounts (e.g. home and work) and/or different operating systems (e.g. Linux and macOS) in sync, while still being able to easily cope with differences from machine to machine.
chezmoi has particularly strong support for security, allowing you to manage secrets (e.g. passwords, access tokens, and private keys) securely and seamlessly using either gpg encryption or a password manager of your choice.
In all cases you only need to maintain a single source of truth: a single branch in a version control system (e.g. git) for everything public and a single password manager for all your secrets, with seamless integration between them.