The chainsaw milling process.
I remembered finding a year or so ago a video demonstrating a technique to mill boards from whole trunks freehand with a chainsaw. So I knew it was possible, I just wasn't sure I could make something thin enough for the projects I had in mind.
I reviewed it and another just to boost my confidence.
Wish I had a level like that second one. That's on my list now.
I laid out the log, and marked out half inch lines with a carpenter's square for my first trial.
My first slice of the edge went well enough, but I quickly gave up on the string part. I also decided I wanted more stability than a bit of scrap wedged under the sides of the log, so I screwed some arms to each end, screwed the arms to one of those pieces of scrap wood, and weighted the ends of the arms with more logs.

The thing didn't budge the entire time I was working.
I went about it like in the videos, using mostly the end of the bar in all cases.
After a few more cuts, though, I realized that the bar itself was a guide that would help me keep things straight.
I would start off by lining up my cut siting along the bar as it just dug into the bark, then go into some deeper cuts at the ends of the log that would actually to continually guide me straight.
Then I'd just work a steady back-and-forth swing, occasionally returning to the ends to extend those cut further, and run the entire bar straight as far along the cut as possible for a moment to confirm the straight.
After a while I'd found a rhythm and the whole thing was in slices before I knew it.
My hesitant practice cuts.
My working boards, though there's hardly a thing to waste except the sawdust.

Freehand/eyeballing the cuts, there's a range of thicknesses, but all between 1/4 and 5/8 inch I reckon. They'll need planing any way to smooth them out.
Anyway, it's not complicated, but I hope this helps others have the confidence to give it a go when they need to.