The fact that there is a commercial version is proof that mperham wants and expects the project to continue sustainably.

That said, the open source version provides more than Monit in a better, easier to deploy package. I think that right there is incentive enough to use it. Plus, if you want to fork it and add your own specific notification channels, here's the source:

https://github.com/mperham/inspeqtor/blob/891517cc0edc6dda8d...