Sounds like you are assuming that I have a server always running for this stuff? That assumption is wrong. I don’t want to run CI servers. If I had servers always running, I would install Jenkins on them and the problem would be solved.
If you are doing deployments, actions etc does exactly that. Run pure bash commands or whatever.
If you want it for other purposes, you essentially want to run a "server" application but don't want to manage a server. Just use serverless? Write a JS function (or some other languages) and the platform will run it when the event triggers.