In "The Geometric Model of Maintenance," someone finally checked the “one month of code, ten days of maintenance” rule against real git history. The number holds up. What it’s made of is worth a look, and so is what you’d need to measure before it tells you anything about your own code.
Scott Chacon and Markus Feilner have introduced GitButler, a tool that changes how developers work with branches in Git: instead of working on a branch, possibly introducing changes that belong in other issues, developers can work on a cohesive codebase and split changes into lanes that make more sense in context, which can make working with git much cleaner.
diffnav gives git a syntax-highlighted display of changes in a navigable filetree, as a natural extension of git-delta. Very nicely done and potentially very useful if you're using git from the command line.
Bram Cohen, creator of BitTorrent, has released "Manyana," a version control system with a new way of tracking changes that reduces the impact of merges to something more manageable and coherent. It's only a proof-of-concept as a VCS, not a replacement of Git, but looks interesting.