Mixed Drinks

Flavoured vodka (Raspberry Absolut or Stoli are faves of mine) with soda and a wedge of fresh lime
Spiced Rum/Bourbon & diet coke with a splash of root beer cordial (root beer not readily available were I live).
Rum with diet ginger beer


Basically switch out sugary mixers for diet versions or soda water. Sugar free cordials can also add a little flavour to white spirits too if you're not too fond on plain soda water.

Suppose I forgot to mention light beers/ciders too, you can also get a lot of low sugar flavoured cider, hard sodas and stuff too compared to what was available a few years ago.

Echoing what the others have said, you can add a shot of whatever liquor you like to a flavored carbonated water (like Bubly) or diet soda.

As a side note, I would NOT recommend the Jordan's skinny syrup drink mixes. My husband got me a set of 6 for Christmas, and they are NOT good. They contain sucralose and they are just way too sickly/fake-sweet for me. I feel like these type of diet/"healthy" versions of foods (like protein powders) aimed towards women feel they need to make them super sweet-tasting for us to like them.

Moscow Mule with zero sugar Reed's Extra Ginger Beer. I cut way back and went AF for 90 days and only drink very occasionally now but that's always been one of my favorites. I make them virgin now quite often for weekend afternoons poolside. I always liked mine with a Tbsp of simple syrup and fresh mint sprigs which isn't traditional, but I find it tasty. For virgin I sub the vodka with club soda.

Zevia makes some nice zero sugar, zero calorie mixers like tonic water and ginger beer. They also have several sodas that work well as mixers.

This may be a minority report, but I'll throw it out here since I don't think anyone's mentioned it. I'm not a huge fan of sweet drinks in the first place, so at reduced calories I'm enjoying a spirit of choice with a dash or two of bitters, and some plain sparkling water. Depending on the specific bitters, a citrus wedge or something like that can be a good add, too. Very refreshing, IMO.

These days, it's not just the traditional Angostura bitters. There are all kinds of flavor profiles of various types available: Citrus or other fruit, herbals, sweet spices (the kind of thing you think of as going in baked goods, cinnamon and such), even vegetal notes.

I'm (sigh) running out of a wonderful smoked apple chickory bitters that's no longer on the market, and working on bottles of lime bitters and cucumber bitters (I love cucumbers!). I found bunches of different types on Amazon, for example. Since you only use mere drops in a drink, they go a long way, and the calories are truly negligible for quite a lot of flavor.

Another option, only slightly higher in calories, is "shrubs" or vinegar-based mixers. Some people think that sounds awful, but if you like beverages with a little tartness, these might surprise/please you. McClary Brothers makes an Apple Pie drinking vinegar as a mixer, for example, that you'd use an ounce in a cocktail, for 35 calories, and it has a nice apple flavor with the usual pie-spice notes in it. They have others (lemon/ginger, pineapple/fennel, cherry, etc.), and other companies make similar products. As a category, these are usually fruity, tart, and lightly sweet.