The main differentiator is the clock source: GNU timeout relies on nanosleep, which pauses if the machine sleeps. This tool uses mach_continuous_time. If you set a 1-hour timeout and close your lid for 2 hours, this kills the process immediately upon wake. GNU would wait another hour.

Written in Rust, ~500KB static binary, and includes --json output for parsing in CI pipelines, as well as extra tiny features.