My brother in law built a frame mounted "sawbuck." The logs are laid on a frame of cross braces, and there is a 16" belt driven circular blade that lowers on the end to cut the rounds. His property has a lot of tall poplar trees, so he drops them and hauls them with his tractor to the table, where he processes everything. No guard over the blade though, so I steer clear of it.
There is also a steam driven set-up in use at Knoebels' Grove Amusement Park in northern PA.