The base itself is a simple mixure: equal parts mayonnaise, plain yogurt, and buttermilk whisked together. What it becomes depends on what you add to it.
Want a light coleslaw? Add lots of dill weed, and add to shredded cabbage. A mix of regular and purple looks especially pretty. Sunflower seeds add crunch.
Want a feta dressing for salad? Add an equal part of feta cheese and lots of black pepper and blend together. For a feta dip, add a bit more cheese until you get the texture you want.
How about a blue cheese dressing? See the feta dressing (you may not need a full part, depending on how much you like blue cheese - we go the whole way). And for a dip? See the feta dip.
Tarragon sauce for salmon? Lots of fresh tarragon into the white base and blend with a stick blender. If you don't have a stick blender you might want to mash the tarragon in a mortar with a pestle before adding it to the base. Oddly enough, this also makes a lovely salad dressing but tastes quite different on the salad than on the salmon. It's also delicious on potato pancake but takes on a third flavor. One time we had all three in one meal - and the tarragon sauce was three different sauces!
To add to its charms, the sauces and dressings made this way are surprisingly stable in the frig. I started by making just enough for the meal. One time I decided to make feta dressing for both nights of a weekend - no problem. Bit by bit we began extending how long we kept some and so far it is good for more than a week.