Remember my UNAN calculator?
Well, another user (who made a calculator for xE# and letter notation up to H) and I have combined ours into one single calculator that can handle both notations. (It doesn't handle combined expressions where one notation is used as an argument for another yet, though.)
This calculator can be found here:
This is also an open project - if anyone else wants to make a calculator for a different notation, they just have to be invited to this project. If anyone is interested, let me know.