For trimming a straight line, say under a fence or against a wall, you can't beat a scythe.
It's only good against posts depending on your skill - you don't want to bury the tip in the side of the post. A wall self-directs it to the right place, by contrast.
It's no good in enclosed corners, which will leave an arc that you can't get to.
But no gas, no noise, no effort.
I get mine from
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(no connection except as customer). I cut an acre of lawn with it, but that's maybe a little extreme if it's not an actual hobby.
A couple hundred random pictures over the years
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Get their grass blade unless you're going to cut woody things, and a straight (not bent) snath.