Interesting. It was free when I got it, and I’m using the latest version without ever having had to pay anything (I don’t even see a price, just an ‘open’ button - and had to open the link from my iPhone to see the price). I guess this is a consequence of how the App Store works …
The editor I seem to to go for everything non-programming related is JOE (Joe’s Own Editor). Its terminal based but when I need to look at or edit a file I always seem to be in the terminal anyway. Its almost always one of the first software packages I install on a new machine.
Given that criteria, and the fact this is for Mac computers (which appears to be the focus), then I nominate Path Finder.
Or better, stretch the “ONE” meaning to one purchase, and get Setapp (though it is a monthly/annual subscription). Then you get Path Finder, Bartender, iStat Menus and many, many more great apps for one reasonable price.
Interestingly, the only “free” applications in my dock are seven I wrote myself to resolve needs I had/have. Oh, wait, Plugins Pro was free, wasn’t it? The only other free app I occasionally use, that isn’t in my dock for that reason, is Handbrake.