For those that enjoy this sort of thing, but don’t enjoy Perl, at the bottom is a link to another blog post about a similar system written in Erlang:
I currently use https://www.chargebee.com/ at work, and it seems pretty well thought out. I know it’s not as exciting as building my own system, but for a lot of businesses, it probably makes sense to start off with something where they’ve thought through many of the details. If nothing else, it’s a good way to figure out what your needs are, and how a fairly advanced system handles some of the details, prior to embarking on the creation of a custom billing system.
It is likely that the billing landscape is better today than it was in 2013, probably due to the existence of articles like this.
I enjoyed reading this post, and the extent to which the authors went to mock around things that sucked in Perl (or in general).
MJD has forgotten more about Perl than most will ever know:
I also found the stories of their success with testing and stubbing rather inspirational, makes me want to try to stub some of the more messy things (like time or delays, or storage) in some code I’m writing at work.