GitLab is Ruby at least, I don't immediately remember any others but there probably are some

• GitHub
• Gitlab
• Airbnb
• Shopify
• Hulu
• Zendesk
• Basecamp, obviously

I know of a bunch of less famous ones, but those are a few of the bigger ones that I’m aware of.

Only people supporting legacy regret.

Ruby was never good. It just got memed enough to make it way into some medium business

Does Redmine count as serious?

Isn't Mastodon Ruby?