A few highlights

Reorganized documentation, with 19 new or revised tutorials.
Automatic MRI fiducial estimation based on MNI Talairach transforms.
Improved plotting support, including new Butterfly plots for PSD epochs, and 3D sensor connectivity plots.
Speed improvements in clustering, coregistration, volumetric source space creation, and other parts of the codebase.
More supported file formats, including curry files, the updated NYU New York 2019 system for KIT, and the new Annotations support for CTF marker files.

In addition, we caught and fixed more than 41 bugs!

Notable API changes

New minimum supported dependencies, most critically Python >= 3.5 is now required.
Complete reworking of EEG channel montage/digitization, including improvements for EEG source modeling with no MRI (surrogate MRIs).
Fixes to volumetric morphing and plotting functions.
Update of the FIF constants.