As part of a team at my last job, I worked on some core features of https://www.salesforce.com/products/experience-cloud/overvie... -- if I'm tricked into a bragging mood I like to say a book got written about it https://www.amazon.com/Practical-Guide-Salesforce-Communitie... The product is still useful to thousands of businesses and transitively their customers, so it's probably the most impact I've made even if it's a shared impact with many others.

Individually, nothing much. Maybe an old python2+numpy re-implementation of a slow matlab script for radar, specifically SAR RMA imaging: https://github.com/Jach/radar_sar_rma I still get the occasional ping about it. A handful of other things have over the years been helpful to a handful of other people, like a hacky jira-to-github-issues migration script, or a simple ranked choice voting counter using scraped web data. That's always nice, but nothing super impactful. I don't mind.