Gwern.net
A huge collection of long-form essays by Gwern Branwen on AI, statistics, psychology, technology, science, economics and plenty of other rabbit holes. Articles are usually extremely well-researched, heavily referenced, and often go much deeper than you initially expect.
raphaelouthier.github.io
Raphael Outhier’s technical blog, mostly focused on low-level programming: C, assembly, kernels, ARM, memory management and optimization. It is especially enjoyable if you like articles that actually explain what is happening underneath the abstraction layers ( if you are here, that might be the case ;) ).
essenceia.github.io/
Julia Desmazes’ blog about chip design, ASICs, Verilog, FPGAs and hardware engineering. The articles often follow real projects from design to tapeout, mixing deep technical explanations with the inevitable chaos of actually building hardware.
lukesmith.xyz
Luke Smith’s personal corner of the web, covering Linux, free and self-hosted software, command-line tools, privacy, languages, books and broader essays about technology and culture. Very opinionated, very personal, and refreshingly far from the usual polished corporate-tech-blog style.