I have seen one brand that was a “tri-fuel”. Of course, one of those fuels is NOT diesel.
If you have diesel, unless I am mistaken, there is no way to make it run on NG or propane.
One of the extreme circumstance fuels that you could use is a “wood gasifier”. Basically, you can run your generator on the gases coming off of a smoldering pile of biomass in a trash can. Plans are online. This has been used before, in WWII.
Diesel has advantages as well, as you can make biodiesel, but I’m not up on the process of creating biodiesel and will leave that to others.
An engine can be dual fuel natural gas and diesel. But it is very expensive and not practical for residential sized units.
I have done it for remote oil field production facilities. But that was a 30MW power plant and the gas had to be compressed to 3,600 psi. They were piston engines, but V18’s and over 31,000 cubic inches. Six 5MW gen-sets; 110 tons apiece.