In our company, we use Substack to write blogs and newletters to our investors / donors / other people interested in AI domain. We talk about how we collect data, principles of making a good codebase for Machine Learning etc.
I use Substack to write newsletter on the latest happenings in the world of technology. I'm a researcher who loves to research about new breakthroughs, new technologies, learn them. I run a community of people who want to learn about new techs and things happening in startup space.