I think anything where lots of parties need to interact with the same service but that service is not very transparent — or abuses their power.

This is a good template for what to look for. Not all domains will need or care an open source solution, but you can look for them based on your domain knowledge.

Highly scalable, reliable and self sustainable AI service which can benefit the humanity in many ways. Currently, the major issue with the closed source AI model's is, you never know what is behind the scene. How things are driven? How the models are built etc. there is a huge potential for making things open source, however due to commercial reason's the big guys don't want to expose, with an exception to companies like "Meta".

a friend of mine had it where he could tweet something and his clothes dryer would turn on. also little barebones (rumba style) robots he put his house plants on that drove around the house to get the most sunshine during the day. another fav of mine he did was repurpose old cellphone camera put in front door peephole to square faces walking up to his front door so he would get phone notif and doorbell rang when someone came close to his front door.

some RRSS descentralized stuff

An automatic printer detector like hp smart but for any printer that is connected to the PC or network