What is Qt Bare Metal?

Is it a way to develop Qt for a bare metal system?

No.

Does Qt run on a system with no OS?

No.

Bare Metal means you usually have a few KB of RAM and ROM.

I think you are confusing Qt (framework) with QtCreator (IDE). Tim Sander explains it clearly here at the Qt Developer Days in 2013.

This plugin is used for developing small software for such platforms, but without using the Qt framework itself.

In other words, you can still utilize the generic functionality of the Integrated Development Environment.

So, it is not a runtime aid, but development and build time helper. You can still use qmake for building binaries for such very small embedded environments.

Here you can find more information in the official documentation.

You can see a presentation about it from Qt Dev Days 2013 here: https://www.youtube.com/watch?v=hrKz63Q_Rf0

It is a plugin to allow you to develop and debug programs for bare-metal embedded targets in the QtCreator IDE.

It doesn't support the Qt framework on those embedded targets.

A lot has changed since you posted this question in 2014. Qt has since released a full suite (bundled with a runtime) called Qt for Microcontrollers that supports app development on minimal hardware with no OS. It can still be deployed on boards with an RTOS. It's not under any FOSS license but you can ask for an evaluation copy.