The author tells us about the Jemula8 :
jemul8 takes an object-oriented approach to emulation. Primarily an educational tool, it aims to provide a detailed description of the internal workings of an IBM-compatible PC.
It aims to reflect computer science concepts, such as Fetch-Decode-Execute, in a largely abstract context, although the only instruction set currently supported is Intel’s IA-32/x86 architecture.
You can read the source code here.
You can see a good example online with MikeOS.
About MikeOS: is a simple operating system with the signature is different and the access to the interruptions and the structure is similar to the DOS.
The Jemula8 is a good example to test your kernels into the online area.
This is a screenshot with the OS named MikeOS and Jemula8 :