[lbittner]

Check out the app called "Tweek". Its exactly what you described here with very little extra fluff.

[al_borland]

Also NotePlan (on the various Apple platforms). Can go by day, week, month, and year, with files stored in a directory of markdown files.

Edit…

I just looked at Tweek, it seems more similar to TeuxDeux, than NotePlan. But NotePlan seems more like what the grandparent was talking about (at least in my interpretation).