$IR M. My 9-year-old son had high hopes for this, to help him stay organized. It worked perfectly in earlier tests under 10.5, but had broken by 10.5.2 in the same way others describe. I saw that a deprecated framework (by now probably removed) is being referenced, hence the freeze.
I advise patience: the author (who I do not know) makes this beautiful app available for free; plus, he's apparently a student himself, right in the thick of things at present. He's likely heard the screams though, and may already be working on a fix. But in the meantime, let's cut him slack and remain thankful for this gift, though it be (temporarily) unusable through no fault of his.
(Version 2.1)