I started this kind of tool-building in grad school, where I implemented a bunch of algorithms from the research literature and combined them together in interesting ways.

Implementing interesting algorithms is a good way to get a feel for the problem space, and it drags a bunch of the UI/UX considerations along with it – once you've created the crux of a particular tool, how do you expose it to a user (or just yourself while testing) in a way that makes sense?

What about it is impressive? Could you elaborate?