Magna Visual porcelain magnetic calendar from MagnaVisual
I love my Magna Visual porcelain magnetic calendars and I use one of them to track exercise by week. I'll indicate the date of the month, time of activity (H:MM), and type of activity ("C" for cardio, "F" for flexibility, and "S" for strength).
I don't use all the magnets that come with it, nor their markers. I love the magnetic markers with built-in erasers by Board Dudes (see the colorful set below).