Although I've been having Keka on my Mac for a few years now, I've only recently started to use it extensively when I've discovered the xz (or txz) format. I've not found another free app that deals with that format.
If you don't know xz, try it and you might be amazed: I've been using 7z for nearly ten years and I thought it was the best option out there but xz can achieve half the size, and sometimes a tenth of the size of 7z (on pdfs in particular)!
The only thing is that it's not predictable on disk images: sometimes you'll gain only 100 Mb out of a 2 Gb dmg, sometimes 1 Gb depending on its content!
Well, I'm supposed to make a review about Keka, but I only use it for xz, I can't say much more, it works perfectly! I'm in the process of converting all my old zip and 7s archives to xz, thanks to Keka. :-)