A self-hosted URL shortener: Shlink - Keep control over all your shortened URLs, by serving them under your own domains, using this simple yet powerful tool. https://shlink.io/

I was very surprised to find this mature, full-featured URL shortener. It's written in PHP and includes Geoblocking so your shortener isn't abused.

A Docker quick-start guide: https://lnk.clifmo.com/ljk13