"in anger" typically means for a real-world, serious project.

Is this a Britishism? I find Americans often are confused by it when I use it.

I'm from New Zealand, so maybe! never knew it was not a thing in America.

I use it too much and it has caused consternation with both American and Egyptian colleagues. Not sure what to reprogram my brain to use because it’s pretty ingrained at this point.

As an American I realize I've only ever encountered it (that I remember) in the context of software development libraries and tools.

i first heard about "in anger" from David Nolen, an American https://www.youtube.com/watch?v=8o01g6C7jWg&feature=emb_titl...

Thanks, first encounter with this expression.

Or perhaps rather they were referring to the classic Erlang in Anger document:

https://erlang-in-anger.com/