When we work on our own personal projects, we espouse the ideals of the agile manifesto:
Processes go right out the window when you're working on a project by yourself. There's no need to do sprint planning or other team ceremonies. Code doesn't need to go through a UAT because you're testing things as you go along.
Has anyone documented their own personal projects? Documentation isn't important when the number of communication paths is zero. A lone coder on a project only cares about working software.
Collaboration with yourself - because you are the customer - is perfect. Whatever you dream up will get implemented.
There is beauty to the flexibility a single software engineer has over a project that only interests them. There's no heavy-handed planning needed, and new ideas can be implemented whenever the engineer desires. Feature prioritization is instantaneous.
Therefore, personal projects are the pinnacle of the agile methodology.