Such services won't realistically be a desktop app, since that pretty much requires them to give away their service and "secret sauce" in a way that's infinitely reusable / copyable for anyone who cares enough to extract it.

The usual situation for services like this is that it either runs on their servers, or you're willing a to pay sufficiently large amount to make it worth the full standard enterprise B2B sales process, a negotiated contract incl NDAs and liability and for them to do an on-site installation. So if you're a big organization that wants to care about trade secrets or classified information, then it can be arranged, but it's not manageable for individual consumers or small businesses.