If you want to have a modern day bare metal experience, playing with microcontrollers is probably your best bet. Buying a board and attaching it to a PC for dev

If you want to have a modern day bare metal experience, playing with microcontrollers is probably your best bet. Buying a board and attaching it to a PC for development has never been easier. Device drivers are usually rather thin wrappers over memory mapped IO. A simple scheduler for multithreading isn't that hard to write and those in FreeRTOS or ThreadX are quite readable despite their production quality feature sets. However, moving up from there to more powerful systems adds more and more (mostly necessary) complexity: address space isolation for robust multitasking, more complicated busses and attached devices, more asynchonous operations, etc. There is no way to have both true simplicity and the comfort / performance of a modern personal computer.