Telegram Bot API (DIY)FREE TIER
free, forever
What I use for every service I ship. 90-second setup via @BotFather, then 10 lines of Python. Phone buzzes when something breaks. Pattern 22 in the boring patterns book covers this.
When something breaks at 3 AM, you want to find out before your users do. PagerDuty is overkill for solo devs.
When the paid tier launches, the 3 people on the waitlist get a one-time email + a free upgrade. No spam. Single email.