JetKVM is much like nanoKVM but a slightly polised version.
What is JetKVM?
JetKVM is a high-performance, open-source KVM over IP (Keyboard, Video, Mouse) solution designed for efficient remote management of computers, servers, and workstations. Whether you’re dealing with boot failures, installing a new operating system, adjusting BIOS settings, or simply taking control of a machine from afar, JetKVM provides the tools to get it done effectively.
As far as I know, these Jets are not available for retail yet, but can be bought via their kickstarter.
Link to the source code: https://github.com/jetkvm/kvm
Link to their website: https://jetkvm.com/
Link to their kickstarter: https://www.kickstarter.com/projects/jetkvm/
Picture of a JetKVM mounted in a homelab, credits to Jeff Gerling.
You can put them behind a VPN and they should be relatively secure. I definitely wouldn't expose it on the web directly, however.
Sure, as long as the VPN itself is secure. Strong passwords/keys, etc. A VPN itself can be a potential security risk, as if it's compromised an attacker can tunnel traffic directly into a network straight past a firewall.
The risks can definitely be mitigated, but if someone's asking for an ELI5 on KVMs, then it may be best to stay away until they have a better understanding of IT infrastructure altogether.