This directory contains source tarballs. Typically, these come from software which either failed to provide a source release alongside their binary release, or don't make regular releases and don't use github or another VCS-backed solution which doesn't automatically generate tarballs.
Please be advised that these tarballs may be removed if they are no longer required (e.g. because that version is no longer being packaged by APK Fission, Alpine, or Adélie.