Puppet Platform 5.5.6 is a bug-fix, feature, and deprecations release that includes updates for Puppet 5.5.6, Facter 3.11.4, and Puppet agent 5.5.6. For details, see the Puppet, Facter, and puppet-agent release notes.
Puppet Server 5.3.5, also going out with this release, includes a new command line tool for interacting with the Puppet CA. For details, see Puppet Server release notes.