Pulse
The system that watches the other systems.
A nightly backup on one of my systems stopped running, and nobody noticed for two weeks. Nothing looked broken. It was simply, quietly, not happening.
Pulse exists so that never happens again. It checks the things that are supposed to be true, constantly, and says something the moment one of them stops being true.
Checks, not just pings
Not only whether the site loads, but whether last night's backup ran, whether the scheduled work is still scheduled, whether the queue drained. The checks are the ones that would have caught the last real problem.
It fixes some things itself
For known, safe failures it takes the first corrective step on its own and reports what it did, instead of waking someone up to type a command they were always going to type.
Alerts that reach a phone
A push notification and an email when something crosses the line, with enough detail attached that the first question is already answered.
It watches its own running costs
It keeps an eye on what it costs to operate and warns me long before that matters. That check exists because it once didn't.
Monitoring is the least glamorous thing you can build and the first thing you regret not having. It is also the thing most small businesses have none of.
It runs on free infrastructure, which is deliberate. There is no good reason for a small company's systems to be unwatched when watching them costs nothing.
What it proves: Anything I hand a client watches itself. That is doctrine, not a feature: a system nobody is monitoring is a system that is already failing quietly.