A linux daemon that you can call scripts more frequently than once per minute. This is extremely stable and runs in production for a number of systems.
frequent-cron is a linux daemon under the MIT License. It is designed to run crons by millisecond in linux. Calls to the script or commands block, meaning that if you have a 500ms frequent-cron and your script runs for 3 minutes, your script will run once every 3 minutes.