Hi, I work in single pilot operations across south Europe with a small single engine prop.
I know that in Italy you can't fly commercial in Single Pilot Operations, you must have a multi engine aircraft with 2 pilots.
You can fly privately with only 1 pilot.
For example, some small jets that can be fly by one pilot only are the cessna citation line: CJ1, CJ2, CJ3 and the new Citation Mustang (C510). I don't remember exactly if also the first Citation (C500-C501) can be fly with 1 pilot only (maybe 500 no, 501 yes).
You can also fly the King Air with 1 pilot.
How about the question regarding the safety:
Of course 2 pilots are better than 1 pilot only, you have to cope with every situation in flight: pilot incapacitation, bad weather, etc.
In Single Pilot ops you may encounter some trouble managing all this thing together.
This is my point of view, but I'm not a very experienced pilot, so I leave the words to the others
