Oh, so many. Right now a lot of things that make use of the Wolfram Language technology stack. Understanding how to use it to teach computational thinking, to do software development, etc. Then using it (as I have for nearly 30 years now) to develop more technology (AI-related things, etc. etc.) I always maintain a stack of projects that I’m interested in. Sometimes it takes decades before the technology I can use gets to the point where it’s actually realistic to do the project (the record so far is Wolfram|Alpha, which had a nearly 40-year span from first conception to actual release). One project I really want to do is seeing whether my way of finding the fundamental theory of physics is correct; hopefully I’ll get to that one fairly soon. And then I have a few hobbies … like studying history of science and technology. Which I occasionally get to indulge: e.g. http://writings.stephenwolfram.com/2015/12/untangling-the-tale-of-ada-lovelace/