Strictly speaking, Facter is an autonomous software project and does not follow Puppet's versioning and release schedule. It is not a surprise, therefore, that Facter 2 was released more or less when Puppet 3.5 was already out.
The first official version of Facter 2 is 2.0.1.
Version 2.0.0 was skipped because previously some 2.0.0.rcX release candidate versions, based on older and deprecated code, were released, and the guys at Puppet Labs preferred to avoid confusion, since the code in 2.0.1 is totally new and unrelated to the one in 2.0.0.rcX.
The main features of Facter 2 (http://docs.puppetlabs.com/facter/2.0/) are: