InvisionApp Blog: one of the few newsletters I actually read because they give you free goodies and worthwhile knowledge
Free Web & Mobile Prototyping (Web, iOS, Android) and UI Mockup Tool | InVision
Atlassian Design Language: Atlassian's framework for design and thinking
Atlassian Design Guidelines | Atlassian Design
Abduzeedo: design, architecture, UX blog
UI Inspiration: Mobile Interactions
HH Design: design community on Medium. Has some great design cases and examples of design processes
A16z: not always design focused but has some dope content on the progression of tech and its future direction. Hear from industry leaders and subject-matter experts in tech.
HighResolution Podcast: leading industry experts on design discuss how it works internally in large companies like AirBnB & Uber