This isn't an exhaustive list by any means and I have most definitely missed some very crucial projects out there. This was an idea I had after watching a YouTube video by The Linux Experiment where he mentioned the idea of a Linux Ecosystem. Why not make it open so that anyone can join? One of us, one of us!
Open Ecosystem Initiative
Open Ecosystem Initiative, or OEI, is an idea of creating an open source, open standard system for bridging together varying devices and software to form an ecosystem to challenge other walled garden competitors. Being able to control things like your TV, Speaker, Thermostat, watch, or other various devices from a user's phone, tablet, or computer. Then even communicating with others who implement this standard so as to bridge the gap.
Solutions Already in the wild
Some of the solutions I've seen so far have been disparate and disconnected. This includes things like KDE Connect or GSConnect for controlling your Android device from your computer or your computer from your Android device. Then the Open Hab project is perfect for controlling and viewing home security and other automation projects. I am sure there are others that I don't know of yet either.
Using things like Matrix's Synapse server is touted as potentially being used for IoT devices or anything that can implement HTTP REST API's sending and receiving JSON. Synapse uses a very basic JSON body and can be customized for a lot of different things routed through Synapse. Synapse can be self-hosted or ran by a provider that the user would trust. Ideally free, but a small fee of $5 USD a month or something to cover serer fees and developer operations time.
For voice automation ideas, one could use something like Simon KDE potentially with Mozilla Project Common Voice to run tasks or other options. Since this would require an always-on, listening device, it would need to be opt-in and also deliver a report upon the user's request to see the listened to or heard items through out the day. Probably show some strange stuff too.
Most of this kind of stuff would most likely need to run on ARM hardware for the self-hosted people because of low power requirements and the affordable price of things like RaspberryPI, Beagle Board, or Arduino. Specialized hardware such as controllers for thermostats would need to be tested and heavily documented while also not bogging down future development and causing head ache when new versions come out.