I've recently come across funktion[1] which is designed to run on kubernetes (which can run on baremetal). Also there is OpenWhisk[2] which is open sourced by IBM. Probably alot more but those are the ones I know off the top of my head.

[1] - https://github.com/fabric8io/funktion.

[2] - https://developer.ibm.com/openwhisk/

No first hand experience with it, but I believe Joyent's Manta system can be, across a cluster of SmartOS machines.

Docker

That's a horrible and flat out wrong answer. Docker simply provides a transferable containerized execution environment for processes with a simple push pull workflow.

Lambda is a fully elastic infrastructure you can build, deploy, and execute functions.

Simply having docker-engine and docker-cli installed on my machine doesn't give me anything close to lambda.