...with a fast, simple UI? :)
So far I've poked at Ardour, but
a) I was pretty sure it was absolute overkill for my simple purposes,
b) The program felt kinda clunky, like if I moved wrong it would crash, and
c) I wasn't sure the program was subsample-accurate.
--
I've pretty much never pursued playing around with audio or music because all the software out there is either undiscoverably obscure, or firmly out of my price range (which is $0, since I a) have no idea if audio editing will even be interesting, and b) don't know what program would be the most appropriate).
After throwing my hands up in the air for the 20th time at Audacity's remarkable sluggishness I stumbled on ReZound (http://rezound.sourceforge.net/ss.shtml) a few years ago and discovered a refreshingly fast tool with VUs that would happily run at 60fps on the ~20 year old machine I was using at the time. (2014 was interesting. I was using an 800MHz AMD Duron with 320MB RAM. And to reiterate, ReZound was completely usable on that machine.)
Sadly, while the most-recent SVN of ReZound does compile on modern Linux, project saving has been broken since the paleolithic era so you have to (re-)export as FLAC to save... and sometimes the edit process subtly injects single-sample gaps of silence which sound like clicks/pops (!), making the program unusable. Not to mention it uses the destructive edit model.
Wish it was in better shape, it's a fairly excellent program.