Salty foods are generally either carby (chips/crisps, fries/chips, popcorn) or proteiny (meat, cheese, nuts.) Most carby snacks have no way to make the salt stick without the fat. Air popped popcorn, for example, the salt just falls off. Ditto microwave or oven crisps. You can reduce the fat and change the fat and that may help. For example oven-baked potato wedges with just a little oil. Air popped popcorn with a tiny drizzle of butter. They sell low fat crackers that are salty but apparently they are high in sugar.
You'll have better luck going the protein route. For those who eat meat, lean meat most certainly exists. I make my own jerky, which is very salty and satisfying. There are also low- and no-fat sliced meats (chicken, turkey, ham) though these need to be kept cool and can't just be pulled out of your pocket for a nibble on the bus. I have seen dried sausages, pepperoni-style, in a snack size and a low-fat variant.
If you have the ability to prepare a little, a salt-lover in my family loves to dip spring onions (green onions - the long thin things that are white at one end and green at the other) in salt a bite at a time.
If you have a home dehydrator, try beet chips: slice beet(root) very thin, lay out on dehydrator trays, sprinkle a pinch of sea salt on each (the juices will make it stick / soak in) and then dry them. I really enjoy these and they are fat-free. Once made, they keep for ages and can be taken with you for an on-the-go snack.