I use 1/2 cup plain yogurt, 1/4 cup mayo, about 1 Tbsp. lemon juice or cider vinegar and 1 Tbsp. honey to make a creamy salad dressing. You can add in some herbs or poppy seeds etc. if you like.
I use plain yogurt instead of buttermilk in muffin recipes. I thin it out a little with some milk. For lactose-intolerance, perhaps a little water or juice to thin it out?
I use it as a condiment for lots of other meals. I top dahl and rice with plain yogurt and chopped cilantro. I mix a little garlic and grated cucumber into plain yogurt for a quick tzatziki; it's great with souvlaki. You are supposed to drain it first if you are making tzatziki, but I often don't bother.
You can use yogurt for smoothies: fruit (frozen berries, mango, banana etc.), some yogurt (plain is fine, DH loves using vanilla), and a little juice and whizz it all up with a blender.