I'm working on a 2d vector editor that'll have that. It's basically a normal editor but where all properties can be expressions that refer to data or other objects. My first target use is for data visualization. What use cases are you interested in?
I don’t need a full CAD constraint solver. Just simple constraints would go a really long way (make X the same width as Y; make A spaced N units from B; etc.). Basically just a glorified spreadsheet where object properties can be accessed and read from cells and objects can have other properties assigned from the cells. Though it doesn’t have to be represented as an actual spreadsheet, of course.