Comment by sam_goody
I use uptimekuma (self hosted) and am very happy - it can text, or just about anything else - as long as you set it up.
Also Tianji[1], self-hosted in the same space.
Of course, these require setup and have to be hosted somewhere. Either another server or deployed to Heroku (Sealos, Render, etc), since they obviously cannot be deployed on the server you wish to monitor!
I've heard a lot of good things - seems like the standard for those that don't mind self hosting and managing the alerts. Our goal with this product is to make sms monitoring easily accessible and hands-free (especially for teams/devs that want to focus on the product/marketing and move quickly). Thanks for sharing these resources.