I'd love automation that could open/close windows and turn on/off my whole house fan based on current outdoor temperature, current indoor temperature, and hourly weather forecast - would be especially helpful when out for the entire evening during the summer. Alas, a solution for actuating the windows does not seem reasonable yet. I could possibly see a system for just automating turning the fan on/off with sensors to ensure the appropriate windows are open being almost as helpful.
I've been kicking this around for a few years as well, and the best I've come up with is a linear actuator mounted... somehow... to the window and window frame. I'm pretty sure it would look at least a bit tacky, and (annoyingly) there's no power near the window I want to open/close, so I'd need to stick a battery over there. Cost, complexity, and I guarantee an auto closing window will get one of my kids fingers at least once (I
think they're smart enough to not do it twice). I've just gone with opening it manually.
However, the approach someone else mentioned - sense that the window is open, turn the fans on? That's worth thinking through, because that is easy to do. Small sensor, wireless transmitter to go across the house on 900 or 433 or something, and a relay at the other end. I like the concept!
I don't understand the water leak thingy. Fix your pipes if you are that worried.
There are plenty of ways to leak water without pipe failure. Not getting a washer drain lint trap fully seated can do it, as can not having the drain tube plug shoved all the way in, as can enough crud around the door or something that gets stuck in the door seal and you fail to notice. All ways our laundry room has gotten wet. We've got a water sensor down in the bottom storage drawer to alert us.
Various
other places I've lived have gotten wet as well, but those were either failed appliances or burst pipes we had no control over. Sadly, the gushing torrents of water were the better clue that something had gone wrong.
In terms of home automation, though? Eh. I've got a Nest and am seriously considering putting something dumber in, because all the "smart" features do is drive me up the wall. Auto-learning? Great, my wife gave the kids a bath at 3PM on Tuesday, turned up the heat in the winter a bit, and now every Tuesday at 3PM, why, turn the heat on! About the only thing of value it does, as far as I can tell, is crank the heat pump up early in the winter so it doesn't have to fire the backup coils (and it's not idiotic about backup coils like some thermostats, where if there's more than a few degree difference between the set point and the current temperature, it uses the backup coils).
Putting in something that could detect I'd opened the window and not fight the fans, though... hrm. That's an idea with promise! And it doesn't need the internet to do it.