Does anyone know of an engine that gives "sub-scores" (e.g., for material, king safety, space, activity) in addition to its total evaluation? Lots of people have wished over the years that engines could help players understand why their moves are bad, and although having access to sub-scores wouldn't be a total solution, it might help. Even if the engine doesn't output these scores directly, if they're part of the evaluation--and if the engine is open-source--a sufficiently interested user might be able to make use of them.
Of course, I'm assuming that something like a "sub-score" is part of some modern engine's evaluation function. They could all be too advanced and/or non-linear for that now.