Max Bronsema
theMusician5044
TWIG - The new theme system
Better Blocks
Breakpoint & Responsive Images
Quick Edit
Configuration Management
Multilingual
Native Web Services
Preview that works
Improved core fields
Enhanced Accessibility
Improved Cache Strategy
3,492 Contributors*
* http://www.drupalcores.com/
Cache tags & Big Pipe
Proudly found elsewhere
Screenshots for the block system go here