I've been on the same mission since I'm on an AI paleo diet where nightshades are excluded. My recommendation below is for cooked sauces. I recently made "paleo" ketchup with dried plums (yes, yes, I know they are called prunes but dried plums sounds so much more appetizing). I've also used them when cooking pot roast. Not perfect, but PDG. Be sure to get ones that have not been coated with seed oil. I suppose you could try fresh plums for salsa - but really any fruit makes a good salsa (mango, pineapple, peach etc) - you could sub in freshly grated ginger for the pepper (since they are also nightshades).

Tips - dice them up small. If you want tomato "sauce" puree with a stick or regular blender after you have cooked them in water/stock.

If your recipe calls for a 14 oz can of 'maters try 6-10 diced plums instead. I try not too use to many as they are carb heavy.

This recipe is really good: http://cavemanforum.com/diet-and-nutrition/nightshade-free-no-mato-sauce-recipe/ I use it for salsa, curry sauce, dips etc.

AI Paleo Ketchup This was an adaptation of Primal 51 Ketchup from The Primal Blueprint Cookbook.

12 diced prunes (sunsweet naturals)

1/2 c vinegar

1 c water

2 cloves garlic minced

1 tsp sea salt

1/8 tsp ground allspice

1/8 tsp ground clove

1/8 tsp black pepper

I cooked the prunes in the water until they softened up a little. You might have added more water if they cook down too far. Then I added the rest of the items and blended with a stick blender. If it is too tangy you can always add a little maple syrup to taste.

I've made butternut squash puree and while it was good, the taste is incomparable to tomato. I don't know if I'll try it as salsa/sauce but here's the recipe if you feel so inclined:

Take 1 butternut squash and chop it up into little pieces but throw out the seeds/pulp (I actually like to heat mine in the oven first with a little bit of water to make the flesh softer). Throw pieces in a blender with milk, salt, and butter (a sweetener such as stevia/honey is optional) according to your taste and desired consistency (obviously less milk = more thick, which I prefer) and puree.

In some cases carrot juice might be an alternative. For instance you could roast minced pork and then add carrot juice to make a tasty sauce. Or cook rice in carrot juice, in case rice is ok for you.

I agree with using winter squash (like butternut) for a sauce, but I'd be wary of using okra. From what I can tell with a quick google search, okra contains solanine, which is one of the reasons that nightshades are discouraged for some people.

I think Nance's idea of pineapple sauce would work. I also think an orange sauce could be quite nice, and you can probably find a lot of recipes to play with online. (And it goes nicely with duck!)

When I used to make tomato sauce at home I made it with a lot of onions. You could saute onions as a base, then add a little orange (plus some zest, perhaps) or pineapple to provide that same smooth base and the sweet and sour flavor that makes tomato sauce so yummy. Add in some green herbs (thyme, basil, and/or rosemary stand out to me as good options) and I think it would be delicious. If the red color appeals to you, you could try cherries instead of or in addition to the oranges.

If I ever determine that nightshades are just too much hassle, I'm transitioning over from salsa to muffuletta olive salad sans pepperoncini. If I could find giardiniera that isn't made with peppers or pimentos, it would be easy. Instead, I give you a recipe suggestion:

Pickle carrots, celery, cauliflower, and onion, however you like. Find some good (non-pimento) green olives and black olives (I like "salad olives" and gaetas for this). Blend your well-drained olives and pickled vegetables in a food processor, add capers and fresh garlic, blend again. Whip in some olive oil, salt, pepper, and oregano (optionally celery seed). Let sit for 30 minutes for the flavors to come together. Eat.

Addendum: if you can find pickled cauliflower by itself, it is ok to mix it with cocktail onions and fresh carrots and celery. If you do this, add red wine vinegar to the mix to make up for the reduced acidity.

The only thing I can think of is pineapple. It's also acidic and has the same tendency to modify/enhance the flavors of other foods. It also tastes nice both raw and cooked.

I love making tropical salsa with mango, pineapple, cilantro, red onion or shallot, but usually put in diced jalapeno peppers which are night shades, but it is tasty even without the heat! It is awesome on coconut flake battered shrimp and chicken fried in butter or ghee.. mmm!

When I think of foods that taste like tomatoes, I think of strawberries. Maybe goji berries too.

Goji berries are nightshades, Harfatum!