I'm transitioning to all-manual lawn care tools, and I love my old reel mower and the sling blade I use to manage high grass. Is there any manual tool I can use for trimming/edging?
Shears or a good old fashioned push armstrong style edger on a long handle. Most any lawn supply will have those.
Here's the armstrong:
Why not go the whole route and transition to stone-age tools. No metal allowed.
Maybe a goat?
You cut a lawn with a sling or kaiser blade? Your lawn sounds more like a heavy underbrush to me. If powered equipment isn't of interest you may want to borrow from the amazonian farmers and simply burn it off.
I would probably gouge out an eyeball before I would go back to a manual edger.
Alternative to a Weed Whacker is at: