Bare Metal Raspberry Pi
Bare Metal Computing
refers to programs that run on hardware without an operating
system. This page talks about Bare Metal things on the
Raspberry Pi Computer.
The Circle library is a C++ framework for writing bare metal applications. It is probably the largest most "modern" thing of it's kind.
David Welch has a github repository full of small bare-metal examples written in assembly, and it has been lovingly documented.