DNF is the new experimental RPM-based package manager that premiered as an experimental option in Fedora 18 and is still working towards feature parity for Yum so that it can be a drop-in replacement but overall it's been making good progress. DNF uses libsolv and Hawkey as its back-end.
With the new DNF 0.4.6 release, the new features include support for "history undo" and the "group summary" command. History undo support allows for package transactions to be reverted. This new release also has internal changes to the CLI for DNF (dnf.cli), better Python 3 support, and many bug-fixes.
More details on the DNF 0.4.6 release can be found from the GitHub-based release notes and a developer blog post.