Simple Operating System programs starting from Bootloader in assembly to Kernel in C, and other programs like OS Calculator, Low Level Graphics etc.
Bootloader contains simple 16 bit as well as 32 bit OS bootloader assembly programs.
Kernel contains C programs for Simple HelloWorld, Keyboard I/O etc... and little bit assembly programs for low level operations.
GUI contains graphics related programs in C for drawing boxes, DOSBox GUI etc.
OS Calculator contains an x86 calculator program capable to run on booting.
Graphics contains simple low level pixels drawing, as well as objects such as Lines using DDA algorithm, Rectangles etc.
Tic-Tac-Toe a simple tic-tac-toe DOS game with boxes.
First read this page before you start: https://wiki.osdev.org/Beginner_Mistakes