Whenever someone mentions building a billing system, I feel compelled to share Mark Dominus' delightful article, "Moonpig: a billing system that doesn't suck":

Whenever someone mentions building a billing system, I feel compelled to share Mark Dominus' delightful article, "Moonpig: a billing system that doesn't suck": > Sometimes I see other people fuck up a project over and over, and I say “I could do that better”, and then I get a chance to try, and I discover it was a lot harder than I thought, I realize that those people who tried before are not as stupid as as I believed. That did not happen this time. Moonpig is a really good billing system. It is not that hard to get right. Those other guys really were as stupid as I thought they were. https://blog.plover.com/prog/Moonpig.html https://blog.plover.com/prog/Moonpig.html