Fost thought immediately goes to acids - Vinegars, Citrus juice (lime), etc. You need to figure out, however, what works with your flavor profile. You can also go with some "sour" sairy (sour cream, cream cheese, roquefort or other non-sweet cheese... A chef I worked for used walnut "flour". The biggest part is to NOT throw your flavor profile in the gutter... E-Z does it until it's to the level of unsweeter you desire.
yeah i mean one would assume youre talking about desserts - puddings, tarts, cakes, cookies? its really not clear
Like one could point out that sugar is a pretty key building block to the structure of certain traditional cake recipes - it does more than just provide sweetness. But that advice and any stemming from it would be utterly useless if youre talking about making..say...a coq au vin less sweet