I am trying a limoncello. Not tart at all really. Just a lemony sweet.
I had half a bottle of Pama Pomegranate Liqueur. Wow. Incredibly tart and sweet at the same time. I bought a bottle more.
I had hoped there was a lemon liqueur that was incredibly tart. I have not tried the large world of liqueurs yet but I don’t think that an artichoke liqueur would be tart. But I saw one.
Ho-boy, sounds like you are gonna have one hell of a hangover. And diabetes. All that sugar.
I seem to remember Midori as being sorta tart. I think they even make sour/tart liqueur that tastes like sour candies. I’m not gonna go look for it though. My pancreas hurts just thinking about it.
Midori is sweet as hell. Not sure if it’s tart but Jeppson’s Malort is downright bitter and astringent.
Limoncello is usually just made from lemon zest. Sometimes it also has the juice of the lemons used to make the simply syrup you cut it with, but I invariably prefer the zest-only versions.
You could try rimming your glass with some sour salt, or even adding some to your limoncello.
I have no idea how that would taste. I mostly use the stuff for popcorn.
Ha. No I’m trying one glass at a time.
I would buy the lowest sugar thing I could get. The baseline for me is the Pama at quite sweet.
It says Fabrizia all natural no ingredients listed. 27%alc by volume.
It’s probably just made from the zest, then. That’s about the right abv for a traditional limoncello.
I don’t understand the bitter appeal.
Lemon popcorn sounds good but doesn’t it get soggy?
I put sour salt on popcorn, not limoncello. 
Not liqueur, but sour beers: barrel aged, gose, brett, Flanders red ale, some lambics, what have you.
Some of the DeKuyper/Bols offerings, like sour apple?
If you’re looking for cocktails, any one that uses actual lemon or lime juice instead of triple sec or something.
Midori is properly enjoyed by being a 21 year old girl and screaming “wooo!!!” It’s weak and sweet.
Cynar. Pretty common in decent bars.
And if you want bitter, there are dozens and dozens of examples.
Well, I like an occasional Campari and soda BEFORE dinner, and bitterness is ALL the appeal in Campari and its ilk.
You might try Deep Eddy’s Ruby Red Grapefruit vodka. Add a little club soda and lemonade.
Not exactly a liqueur, but Limdemans Framboise is like a raspberry Jolly Rancher.