I've been thinking for years about a safer alternative to chain saws. Something along the lines of a carbide coated wire driven by an electric motor and battery. Strap it to the tree, turn it on, walk away and some minutes later the tree falls down. The main difficulty is in how to drive the wire. Using friction would create fast wearing parts. Maybe a chain could be used instead of a wire. It could oscillate back and forth, instead of having to be wrapped and spliced to form a circle around the tree. It seems really strange that no one has come up with an alternative to chain saws for decades (except for large scale trucks that can process whole trees.) For small trees and branches even a sawz-all is safer than a chain saw. Inspired by spending some time sharing a hospital room with a guy who had a chain saw accident, but I still haven't come up with a workable idea. Maybe someone else can.