https://www.isthereanydeal.com/

This site not only shows you historical data on steam, but on 3rd party sites and other launchers as well (fully configurable). And it’ll send you a mail is any game in your wait list meets any of the criteria you set (e.g. under $10, lowest historical price, etc.)

I don’t have HVAC, so I’m just using it to see when the air at my desk is getting stale so I remember to open the window. I mostly use homeassistant for the configuration, although I might also set up a notification at some point (I only got my sensor 2 days ago)

Very nice.

It’s missing CO2, but those are expensive so that’s understandable. If you need one of those, I think https://www.airgradient.com/ is a great choice.