other possibilities to substitute for pineapple in that salsa:
1) fresh rhubarb 1/4" cubed, some extra rhubarb juice, and sugar
2) jicima cubed and gently steamed, tamarind paste, and lime juice
3) big blueberries, halved, and sugar
4) tart green apples cubed plus sugar and a little apple cider vinegar
Mango, specifically green mango. You'll get a similar texture, some tartness, and it is already a widely used thing in salsas. You could easily pick how tart you want it by switching to s slightly riper Mango.
Your pineapple in a salsa is going to add some sweetness, a lot of acidity, and crisp chunks that will be important to the texture.
While other tropical fruits would be have the sweetness and interesting flavor, I can't think of anything that adds the acidity and texture. When ripe, mango and guava are quite soft and although there are delicious mango ...