As the title says. I want a light, free software so that I can execute a program or command to start a program on, say, 15 machines, simutaneously.

I would prefer one that works over the internet, but also one that would signal over a wifi network as a backup.

Finally, if there is a way to achieve simutaneous program execution without unlocking a computer or complicated setup, please let me know, that would be amazing.

Thanks in advance, /wsr/!