I know of a couple of rather fancy, proprietary 2-way radio trunking systems products that use local MS SQL on the back end, to keep track of configs for individual subscriber radios and system configurations for the radio repeaters.

(What's that? Well, if you ever walk into a place like a gigantic oil refinery, you'll see a bunch of people working there. If you look long enough, you'll notice that each of them have an expensive-looking radio ("walkie talkie") on their hip. Some of those radios may be my fault -- and of those that are, there's an MS SQL database that knows exactly how it was programmed. But I didn't pick it; that's just how the system operates.)