Zuora is a well-known Enterprise-scale commercial option that displaced many others as “SaaS” took off several years ago (and its associated accounting standards).
Depending on complexity, Netsuite can address some moderate scale use cases. Stripe, Chargebee, etc address more of the SMB-scale needs.
Yeah, usage rating and billing systems get wildly complex. Especially when you start considering edge cases- beyond leap years and handling time zones, things like a billable event spanning days (run a few minutes just before midnight), etc.
A Chick-fil-a near me recently remodeled and moved to a dine-in model where you don’t order at a counter- you sit down and someone comes to take your order on a tablet. I suspect we’re 5-10 years out from McD and others trying to incentivize tipping for order takers, and eliminating dine-in from some locations entirely.
McD fries just aren’t the same when delivered!