title_body: Could you list healthy, unsweetened coffee flavouring syrups?
upvoted_answer: The brand MiniSyrup seems to meet your requirements. From their website,
  
  
    SUGAR/SWEETENER/CALORIE FREE. Unlike the big bottles of syrup that are crammed with sugar or artificial sweeteners like sucralose and aspartame, MiniSyrup Flavor Shots are the first completely unsweetened flavoring made to flavor your favorite beverages like brewed coffee, hot chocolate, lattes, fountain sodas, tea and more. This gives you complete control over not only the flavor in your beverage, but also your sweetness. [1]
  
  
  They don't seem to have nutrition information on their website, but myfitnesspal lists the nutrition information for some of their flavors. I'm not sure of the validity, but as you mentioned in a comment you can reach out to MiniSyrup for more information.