Privacy
Short version: nothing about you is collected, stored or shared.
The app
Spider Solitaire has no account, no analytics and no ads. Your saved game, statistics, achievements and settings stay on your Mac in the SpiderSolitaire folder inside Library, Application Support.
The one network request is the update check. When Check for updates automatically is on (Settings, General), the app asks GitHub's public API for the latest release at most once a day at launch, and when you choose Check for Updates. The request carries no identifier, only the app's name and version in its User Agent header, as GitHub requires. GitHub's own privacy statement covers what it logs. When you choose Install, it also downloads the release zip and its checksum file from GitHub. Turn the setting off and the app makes no request unless you ask.
This website
The site is static and hosted on GitHub Pages. It sets no cookies, runs no analytics and loads nothing from other servers: fonts, icons and images are all files on this site. GitHub Pages may keep standard server logs, as described in GitHub's privacy statement.
Questions
Open an issue on GitHub.