- Nothing. Yes, nothing. Simply do not track anything, that may be the best way to go as it respects visitors' privacy.
- Matomo (previously called Piwik): seems to be the best of its kind. Well maintained, full of features. Big focus on its commercial offering of hosted service. Matomo on GitHub.
- Open Web Analytics (OWA): looks less fancy. Seems to be more community oriented, no business around. Open Web Analytics on GitHub.
- Fathom: maybe the newest kid in the neighborhood. Built with Go and Preact (a smaller React-compatible JS library, first time I hear of it). Fathom on GitHub.
Other pieces of software might be worth a look. No software also deserves a lot of consideration.