openHAB

Great home automation system that offers total control for enthusiasts and experts alike. I love being able to program my automation rules with Ruby programming language in openHAB. It also supports JavaScript, Python, and Blockly graphical programming. If you don't know how to code, you can use its web interface to set up your automation and rules just as easily. Another aspect I love about openHAB is that it's 100% free and 100% open source. No monthly fees of any kind. No "community vs premium" tier. It's just free for all! Furthermore, it doesn't collect your data in any way. It doesn't even collect any usage statistics. It is simply built and maintained by passionate people who are using it for themselves.

openHAB has a bit of a reputation that it has a very steep learning curve and only IT nerds can use it. In the early days of openHAB (1.x) this was true - however, since then a lot has changed and the current version (4.x) offers completely different experience and makes it much easier to start with. However - the strong point of openHAB compared to other solutions is that it is not related to a company and that also remote/cloud access is free. But the power and flexibility of the system still has its price tag - if you would like to automate your home and you are willing to first read a bit of documentation you'll get a very flexible and stable system that you can completely customize to your needs. With the new UI & different rules engines (including blockely and node red integration) it is easier than ever to start with your automation. And when you get more ambitious and your requirements towards the flexibility of the system openHAB will offer it. There is a helpful community and the documentation improves continuously and already is comprehensive. Unfortunately the product lacks a bit in the marketing area and is not as visible as other products - but if you're willing to invest a bit into learning the basics you'll not be disappointed. I use it since version 1 (~10 years now) and never regretted it - and last but not least the migrations between versions was always smooth. The community is friendly and helpful in case you get stuck.

It is a large platform and it can be complicated at first when getting started. However, once you learn the platform there is almost nothing you cannot accomplish with it. One of OH's main focus is on automation (when X happens to Y but only if Z). It has a friendly and helpful user community and is undergoing active development. I highly recommend.