Is there any material natural or otherwise a free floating liquid that can exist in space?
No liquid can be completely stable in a vacuum, since all liquids have some non-zero vapour pressure, and so will evaporate at some rate. However some liquids have an exceptionally low vapour pressure, and so can be used in a vacuum.
If a location could be found at which it was warmed sufficiently to remain liquid (in deep space it would just freeze, whereas too close to the sun and its vapour pressure would rise) it could remain in a liquid state for some time. Not indefinitely but it could be stable for a while.
My answer is: superionic water, at high pressure and low temperature. During the superionic phase, the hydrogen and oxygen within water molecules behave bizarrely; hydrogen ions move like a liquid, inside of a solid crystal lattice of oxygen.
Derivation of answer, and references:
Any element or molecule will evaporate (essentially boil) in low enough pressure, even at extremely low temperatures; albeit slowly (by human standards).
Both extreme pressure and low temperature is necessary to prolong the lifespan (duration) of an element or molecule's liquidity.
Something contained must also be "free floating" (to comply with the terms of your question) - thus suggesting liquid hydrogen (or deuterium) seems a stretch, but it's a clue for the direction to look.
From the article: "Settling Arguments About Hydrogen With 168 Giant Lasers":
At ultracold temperatures, below -423 degrees Fahrenheit, hydrogen condenses into a liquid. It also turns into a liquid at higher temperatures when squeezed under immense pressure. The molecules remain intact, and this state of liquid hydrogen is an insulator — a poor conductor of electricity.
Under even higher pressures, the molecules break apart into individual atoms, and the electrons in the atoms are then able to flow freely and readily conduct electricity — the definition of a metal.
Liquid metallic hydrogen does not naturally occur on Earth — except possibly at the core. But at Jupiter, the solar system’s largest planet, most of the hydrogen could be flowing as a liquid metal and generating the planet’s powerful magnetic fields.
Preventing freezing (solidification) of the hydrogen is the key, and the use of pressure will alter the phase change diagram.
The article: "Two Pathways to Metallic Hydrogen and Deuterium" (by the Silvera Group, Department of Physics, Harvard) has some photos of liquid hydrogen:
"Images of hydrogen at different pressures and low temperature showing the progression from a transparent molecular solid to a black semiconducting solid to a brilliant shiny metal of hydrogen."
It was also realized that at a lower, but still high pressure and very high temperatures, there is a temperature driven transition to liquid atomic metallic hydrogen (LMH). This liquid-liquid phase transition is sometimes called the Plasma Phase Transition or the PPT. We have determined the phase line for LMH and liquid atomic deuterium for several values of P and T, as well as optical properties and optical conductivity. We observe isotopic differences in the phase lines.
LMH is the principle component of giant outer planets such as Jupiter and gives rise to its magnetic field via the dynamo.
BUT, there are the terms of your question (which the answerer ought not to fudge on): "Is there any material, natural or otherwise, a free floating liquid that can exist in space?"
So simply pressurizing hydrogen didn't seem to meet the requirements of "free flowing" (unless you'll accept it as one answer) - but it hinted at the direction I should look.
The clue led me to superionic water, at high pressure and low temperature.
From the Nature article: "Experimental evidence for superionic water ice using shock compression" (Nature Physicsvolume 14, pages297–302 (2018)) and also written up at LiveScience: "This Ice Is Nearly As Hot As the Sun. Scientists Have Now Made It on Earth":
It's both solid and liquid, it's 60 times denser than ordinary water ice, and it forms at temperatures almost as hot as the sun's surface.
It's superionic ice — and for the first time, scientists have made it in the lab.
This high-pressure form of water ice has long been thought to exist in the interiors of Uranus and Neptune. But until now, its existence was only theoretical.
Scientists first predicted the existence of a weird water phase that makes the substance both solid and liquid at the same time 30 years ago. It's also way denser than ordinary water ice because it forms only under extreme heat and pressure, such as those found inside giant planets. During the superionic phase, the hydrogen and oxygen within water molecules behave bizarrely; hydrogen ions move like a liquid, inside of a solid crystal lattice of oxygen.
Making the ice was complicated. First, the team compressed water into an ultrastrong cubic crystalline ice, in a different crystal form than what you see in ordinary ice cubes. To do that, the researchers used diamond anvil cells to apply 360,000 pounds per square inch (2.5 gigapascals (GPa) of pressure; that's about 25,000 times the atmospheric pressure on Earth). Next, the researchers heated and compressed the cells even further, using laser-driven shocks. Each crystal ice structure received up to six laser beams of more than 100 times that high pressure.
"Because we pre-compressed the water, there is less shock-heating than if we shock-compressed ambient liquid water," Millot said. The new method lets researchers "access much colder states at high pressure than in previous shock-compression studies."
Once the superionic ice was ready, the team moved quickly to analyze its optical and thermodynamic properties. They had only 10 to 20 nanoseconds to perform the work, before pressure waves released the compression, and the water dissolved. And the results were bizarre. They found that the ice melts at an extraordinary 8,540 degrees Fahrenheit (4,725 degrees Celsius ) at 29 million pounds per square inch (200 GPa) of pressure. That pressure is about 2 million times the atmospheric pressure on Earth
The new findings could provide a peek inside the interiors of planets such as Uranus and Neptune. Planetary scientists suggest these worlds' innards are composed of up to 65 percent water by mass, plus some ammonia and methane.
Thus, hydrogen can be liquid and "float freely" in space - but only in a lattice of oxygen, under the extreme pressures, at the core of one of our gas giants (or other similar objects in space).