Http
https://github.com/vinbero/vinbero
Bluetooth
GPIO
GTK (gui)
https://www.raspberrypi.org/magpi/issues/c-gui-programming/
OpenCL
https://github.com/doe300/VC4CL
Gui without Desktop
https://medium.com/@avik.das/writing-gui-applications-on-the-raspberry-pi-without-a-desktop-environment-8f8f840d9867
http://raspberrycompote.blogspot.com/2012/12/low-level-graphics-on-raspberry-pi-part_9509.html
https://github.com/matusnovak/rpi-opengl-without-x
Blowfish
https://github.com/HybridEidolon/saredit/tree/master/src/blowfish
Pixel Art Editor
https://github.com/mananapr/pxlart
Hex Editor
https://github.com/krpors/hx
OLED Controller
https://gecko05.github.io/2019/06/23/rgb-library.html
Example VPN
https://github.com/jedisct1/dsvpn
Linux System Programming
https://xmonkee.com/posts/LinuxSystemProgrammingCh1-4