Grillo or BCS or used Gravely equipment. I started off with a Gravely. Couldn't use it (12 hp model) until I found and installed some wheel brakes on it. Even then, it's more a handful than a 4wd sit-on tractor.
After 4 years, I bought a 4wd JD diesel. The Gravely had issues in getting back up our back hill at times or skidding down it at times, even after I put dual wheels on it.
Ralph