Rinse blueberries and remove any stems. Pat them dry. Place two cups of the berries in a medium bowl. Reserve the remaining cup of blueberries for later.
Rinse an apple and pat it dry. Without peeling the apple, use a small knife to slice off large pieces around the core. Chop up ⅔ of the apple and add it to the bowl with the blueberries.
Rinse a red pepper and cut out the stem. Cut the pepper in half and remove the membrane and seeds. Chop up half of the pepper and add it to the bowl.
Peel and chop a small red onion until you have ⅔ cup. Add it to the bowl.
Rinse the jalapeño and cut off and discard the stem. Cut the jalapeño in half. You can use some or all of the seeds if you want a hotter salsa, or discard them for a more mild salsa. Chop up the jalapeño, adding it to the bowl. Don't touch your face after handling the jalapeño, because it will sting. Wash your hands well afterward.
Rinse the cilantro and shake off the water. Use scissors to cut off some leaves until they measure ⅓ cup. Add the cilantro to the bowl.
Add the lime juice, applesauce, sugar, hot sauce, salt and black pepper. Toss everything with a spoon to mix it. Add the mixture to the bowl of a food processor fitted with a chopping blade (or add it to your blender). Gently and briefly pulse the mixture one or two times. If needed, pulse it again, just until everything is chopped. (Be careful not to let the food processor or blender run too long, or you'll end up with all liquid.)
Drain any excess liquid in a fine mesh strainer and return the chopped salsa to your mixing bowl. Stir in the remaining cup of whole blueberries. Refrigerate the salsa for an hour before serving, ideally. Give it another stir and taste it to see if it needs any sugar or seasonings.
Serve it with tortilla chips or use it as a topping for grilled salmon, chicken or pork. Refrigerate any leftovers for up to four days.
To make this spicy hot, include some jalapeño seeds.
If serving as a topping (without salty chips), you'll need to add more salt.
If your blueberries aren't sweet enough, you'll need to add more sugar.
If you want to tone down the heat, add more sugar and extra blueberries or apple pieces.
This recipe has not been tested for canning purposes, so it would not be safe to can it.