- CPU, ISAs and assembly languages for different architectures
- operating systems
- audio programming (DSPs, harmonic analysis, etc.)
- graphics programming
- compilers and programming language implementation
- media codecs (audio, video, images)
- media processing (e.g. text to speech or speech recognition)
- networking (IP, TCP, etc.)
- embedded systems
- cryptography (or implementation of cryptocurrencies like Monero)
- text rendering (creation of fonts and display on screen)
- signal processing (e.g. wireless or satellite signals)
- telecom systems (5G, 4G, etc.)
- positioning systems (GPS, GLONASS, etc.)
- any other topic the community thinks I have missed out
find "Building an 8 bit breadboard computer".