For example, a cli app that creates/set-ups something could add confetti/fireworks to it's "done, go have fun" message.

This will make is cool confetty highly accessible for everyone :-)

I use goreleaser for all my go projects to acheive the same

https://goreleaser.com/

Example repo (my repo): https://github.com/kishaningithub/shopify-csv-download/releases

Let me know if you are fine with this, i can work on a PR for the same :-)

While the firework is launching the trail glitches out and doesn't animate correctly

Would be nice to be able to pass a message to confetty -m "You win!" that created some kind of modal or title to show what is being celebrated

I was just a bit confused when I found out that pressing any key casts a new confetti, but pressing arrow keys doesn't do anything different from any other key.

I'd intuitively expect arrow keys to move the confettis in any direction. Or at least left/right, which would be even more expectable from fireworks since they're launched from bottom to top. By the way, moving fireworks horizontally "mid-air" just sounds dynamic and cool.

I have not tried to implement this myself (yet?), but since fireworks are launched from a random point that is (!) available on the screen, and the confettis are centered relative to the screen, I take it as not too hard of a task.

P.S. The confettis remind me of cmatrix

It would look like this:

▄ │ │ │ │ │ │ │ │ │ │ │ │ │

it seems as though Github doesn't connect the lines, but the characters use up the full space so there would be no gaps

I have a screenshot although I had to use Discord for filesharing
example