I have the GoControl zwave thermostat. It’s very barbones and has no real smarts on it’s own but can be fully controlled by zwave. This is what I was looking for as I wanted full control over the algorithm, but if you want to it have more intelligence without having to write the code yourself you should consider other options.
I started self hosting many years ago when the company I worked for got new workstations and sold the old ones for next to nothing. It was a very powerful machine but I payed the price every month in electricity. I am now running a bunch of services on 2 mini pcs (each was about $250 USD) with laptop cpus and my electricity usage is way down (like 45 watts for both machines, router, and switch).
There will be a steep learning curve, but I highly recommend learning docker (especially docker compose) and how to setup a reverse proxy. The self hosted communities are very helpful and can answer more specific questions as they come up.
Memos fits a wide variety of uses and is the first note system that has clicked for me. I use it for quick notes so I don’t forget things, journal-like entries, save for later (like Pocket), shopping lists and other todos.