There are 2 repositories under mini-os topic.
Sqrt OS is a simulation of an OS scheduler and memory manager using different scheduling algorithms including Highest Priority First (non-preemptive), Shortest Remaining Time Next, and Round Robin.
DJ-LaVa is a replica of Mini OS which is made using Windows Forms Application. Its hard coded in C# and is consortium of apps like Calculator, Calendar, Browser, File Manager, Maps, Media Player, Notepad and a Shell.
Simplest operation system for stm32 board and m4 processor
DLXOS Introduction at https://engineering.purdue.edu/~ee469/labs_2021/