Let's imagine you have a real-time problem that you can solve with the Raspberry Pi hardware but you need something much faster than an Arduino. Is it possible to bypass the OS of a Raspberry Pi to have used some kind of bootloader like an Arduino, and run with the same structure in real-time as with Arduino (i.e. no time-sharing), but much faster?
That is very much the premise of Ultibo.
What is Ultibo?
Imagine if you could have the simplicity and freedom of Arduino with the power and features of a Raspberry Pi. With the ease of a microcontroller and the flexibility of a real computer, Ultibo gives you a platform for creating anything without the limitations of a traditional operating system.
If Ultibo is not what you want there are plenty of other bare-metal (no operating system) examples for the Raspberry Pi.