Puppet master is a Ruby application that compiles configurations
for any number of Puppet agent nodes, using Puppet code and various
other data sources. (For more info, see Overview of Puppet's
Architecture.)

Puppet Server is an application that runs on the Java Virtual Machine
(JVM) and provides the same services as the classic Puppet master
application. It mostly does this by running the existing Puppet
master code in several JRuby interpreters, but it replaces some
parts of the classic application with new services written in
Clojure.