The Orbital Index, for weekly updates about the space industry: https://orbitalindex.com/

Bitcoin Optech, for weekly Bitcoin news: https://bitcoinops.org/

Lil'log, for well-written content on topics in AI: https://lilianweng.github.io/lil-log/

The Gradient, for the same reason: https://thegradient.pub/

Slate star codex, no explanation needed: https://slatestarcodex.com/

I also subscribe to releases for Python, Julia, Rust, Matrix, Jami, LBRY, and a few others.

And a shameless plug for my own blog: https://jarbus.net

I use newsboat as my RSS reader, lovely way to check the day's feed from the terminal.