Nano quickly comes to mind. There are others that fit on this playing field too.
Discussion
How many people use Nano?
I mean if we're talking real world practical use here, we must take into account how battle tested a product is and how widely adopted it is.
Bitcoin Lightning is used to accept Bitcoin payments as legal tender in El Salvador.
Nano is accepted... where?
It's still fast and cheap and available. It works and has worked for a long time just as fast and just as cheap.
Being popular doesn't make it less or more so.
I'm talking about how battle tested it is, not popularity.
But adoption is also important because these are meant to be currencies. I could invent some hypothetical super coin that's amazing technologically, but if no one adopts it, it's functionally useless.
It is a matter of fact that Bitcoin is, well, Bitcoin. Even my grandma knows what it is. As I said, adoption is key when you're asking someone to accept something as currency. You're asking them to trust that it has value.
To me it makes no sense to gamble on whether Nano will ever be adopted for payments because it's cheap and fast when lightning already allows me to make cheap and fast payments in the most recognised and valuable cryptocurrency in the world.