Underneath, Notify! is just a URL. Anything that can open one can send you an alert, and where that alert lands is entirely your choice. Open it in a browser and be running in about a minute, or install the iOS app on an iPhone or iPad for the fullest version, watching sites on the device itself with Live Activities and beacons. A Mac and an e-ink panel work too. Every route below is free forever and none of them ask you to make an account.
They all speak the same contract. Whichever you pick, you get a webhook URL of your own, and anything that can make an HTTP request can use it. Mix them freely: one script can light up a browser, a phone and a wall panel at once.
The receiving end is the only part that ever needs installing. Sending is a plain HTTP request, so a cron job, a Bash one liner, a GitHub Action, a Synology box, a Home Assistant automation or a service like Zapier, Make or Uptime Kuma can all reach you with no library, no SDK and no key to apply for.
Ready made paths for the services people ask about most, plus what the community has built on top.
Start in the browser. It takes about a minute, costs nothing, and you can add a phone, a Mac or a panel later without changing a single URL you have already given out.