ImpressCMS 1.3.8 contains updates for external libraries and bugfixes, some of them backported from the ImpressCMS 2.0 developments.
If you are installing a new site, use the impresscms-1.3.8.zip archive.
If you are upgrading an already existing site, please use the impresscms-1.3.x-to-1.3.8.zip file to conserve your configuration.