1. Networking: https://github.com/AbhinavMir/networking
2. Databases: Learning about recovery via ARIES is enough for now - https://www.shreya-shankar.com/aries/
3. Algorithms and Complexity: https://hackmd.io/@augustradjoe/algo-complexity
4. Cryptography: https://hackmd.io/@augustradjoe/crypto-guide
5. Compiler theory: https://hackmd.io/@augustradjoe/compiler-theory
6. Operating Systems: Not my expertise, but I learnt a lot via Broken Thorn's follow along, as well as building an OS in Rust. On top of that, doing a bunch of CTFs helped me. Guide on [that](https://hackmd.io/@augustradjoe/ctfs). More advanced OS needs you to study locks, virutalisation etc, which isn't my expertise (yet!).