The Java implementation of the Aion kernel is the original implementation. Learn how to install and configure it here.
If you want to get up and running quickly, check out the Docker Images section. These images allow you to spin up an Aion Java kernel on any operating system with Docker installed.
Aion has lots of different aspects and products, and everything can get a bit confusing. If you think of the Aion network like a train, the kernel is the engine. It's the thing that does all the hard work, computing all the processes, and pulling the rest of the network along.
Things like the Aion Virtual Machine, local nodes, and third-party hosting services all use the Aion kernel. They are just different methods of hosting the same thing. The Aion White Papers provide a deeper look into what the kernel is and how it works.
This section of the docs goes over how to configure and interact with the kernel directly. If you're looking to develop the Aion kernel itself, or mine on Aion, then this section is for you! If you're just looking to create some Dapps, then you can leave this section for now.
If you want to get involved with the Aion Java kernel development, take a look at the Github repository.
If you're interested in mining on the Aion networks, refer to the Mining section.