One of the early selling points of the Falcon 50 was its capability to operate off of unimproved runways, meaning grass, dirt or gravel. However, a service bulletin (SB) had to be complied with for approval for such operations. When we ordered our new Falcon 50EX in 2004 we asked for this service bulletin to be complied with, Dassault informed us that the parts for compliance to the service bulletin were no longer available and that of all the Falcon 50s built only one had the service bulletin installed and they dropped the program.
From what I recall the modifications involved the nose gear, nose wheels, main gear tires and the flaps. I could be wrong on this.
There were also videos of the Falcon 10 made by Dassault operating off of unimproved runways, however, I don't know if any Falcon 10s were approved to do so operationally.
I have operated King Air 200s and MU-2s on gravel runways in Canada and Alaska. You just have to be careful during reversing after landing and be slow adding power on takeoff to avoid damaging the propellers.