Docker-Swarm, Kubernetes, Mesos & Core-OS Fleet

I am relatively new to all these, but I'm having troubles getting a clear picture among the listed technologies.

Though, all of these try to solve different problems, but do have things in common too. I would like to understand what are the things that are common and what is different. It is likely that the combination of few would be great fit, if so what are they?

I am listing a few of them along with questions, but it would be great if someone lists all of them in detail and answers the questions.

1. Kubernetes vs Mesos:
2. This link

What's the difference between Apache's Mesos and Google's Kubernetes

1. provides a good insight into the differences, but I'm unable to understand as to why Kubernetes should run on top of Mesos. Is it more to do with coming together of two opensource solutions?
2. Kubernetes vs Core-OS Fleet:
3. If I use kubernetes, is fleet required?
4. How does Docker-Swarm fit into all the above?

#kubernetes