I use Home Assistant (https://www.home-assistant.io/). It has an integration for lots of manufacturers. Single app, single entry point, cross manufacturer automations.
But it is available as a plug-in appliance, and they're getting better and better at the Just Works aspects all the time.
And in a world where everything is relative, it's a hell of a lot easier to get started with Home Assistant than it is to get started with something like KNX or Crestron.
I have all kinds of widgets around me at home that are the products of successful companies of various sizes, and that are so niche that 95% of people would probably never seek to own such widgets themselves. Most probably aren't even aware that widgets like this exist in their universe. But the remaining 5%? They know about the widget, and they want one (maybe more than one).
There's ~149 million households in the US alone. 5% household penetration would require ~7.5 million widgets.
It sure is easy to imagine ways that a person and/or a company can sell just 7.5 million widgets and ultimately be financially unsuccessful, but it's also easy to imagine ways in which that would work out just fine.
But that's just meandering digression. :)
The Open Home Foundation had revenue of CHF 8,836,394 and expenses of of CHF 7,352,798 in FY 2025[1].
Is that small potatoes in a world with trillion-dollar companies? Yeah, it's certainly not ginormous. Is that successful? I personally think that it is.
I'd much rather have an open version of Apple Home or whatnot, even if I paid for it. I really don't want to spend a bunch of time dicking around with home automation - I want it to simply do what I want it to do.