[blueblisters]

Shopify (along with its millions of shops) is probably the biggest user of Rails (with Ruby) in production. Aside from them, not sure who uses Ruby at that scale.

[Cthulhu_]

https://stackshare.io/rails is a reasonable source to see what company uses Rails; notable entries are Github, AirBnB, Twitch, etc. Mind you it doesn't really say what / how much of those things are made with Rails. Github definitely uses it a lot though: https://github.blog/2019-09-09-running-github-on-rails-6-0/

[strzibny]

Stripe, GitHub, GitLab, Hey, ...