That's one of the Halstead metrics (https://en.wikipedia.org/wiki/Halstead_complexity_measures). It's all based on the number of operands and operators in your code. To make things simpler and practical, FTA combines these metrics with cyclomatic complexity (effectively the number of logical paths), normalizes them and produces a single number with accompanying 'assessment'.
OP, are you aware that the React team are testing their own compiler for React? Not to say your project is obselete, just want to make you aware. The team talked about it at React Conf 2021 (see youtube videos), currently named React Forget.
It's specific to a UK audience but I made a tool that, at least in my mind, is better than the existing tax calculators for UK workers, and goes a bit further with letting the user forecast potential wealth building, using a very popular approach (index funds using ISA wrappers).
It's worth pointing out that Gitlab's hosted service has suffered a myriad of pretty disastrous outages and problems over the past 12 months. In my experience, it's been totally unreliable compared to it's rivals. So I wouldn't say that they are a leading example of success just yet, although they certainly have a good shot.
One thing I personally value in something like this is the ability to opt in or out of features, so that I could use it a fairly low level set of utilities (think large user-facing piece) but also as a full-blown opinionated UI library with lots of things ready to go (think internal piece).
That's an interesting idea, thanks. We wanted to avoid any concept of registration (ie all appointments are currently 'checkout as guest'), since it's an experience barrier, but Fb/Tw/G+ are good human verification tools.
Full disclosure though, it doesn't currently support GIAs. That would typically come after you've filled a S&S ISA which doesn't apply to most people.