I recently learnt that my former coworker Jonny took his efforts around his own monitoring system Bloonix and moved to self-employment.

If you're considering to outsource your monitoring consider Bloonix. As a plus all the code is open under GPLv3 and available on GitHub. So if you do not like to outsource it you can still build up an instance on your own. Since this has been a one man show for a long time most of the documentation is still in german. Might be a pro for some but a minus for others, if you like Bloonix I guess documentation translations or a howto in english is welcome. Beside of that Jonny is also the upstream author of a few Perl modules like libsys-statistics-linux-perl.

So another one has taken the bold step to base his living on free and open source software, something that always has my admiration. Jonny, I hope you'll succeed with this step.