I've messed around with the API and was for a short while developing a Lowest Light application so that you would know if a blue engram you got is higher than the lowest light level you have in that category (for infusion purposes). From research for this I learned that Weapon objects do not return with some of the information you would expect it to have. For example, weapons don't have a rarity property that indicates whether it's common, uncommon, rare, legendary, exotic, etc. Instead, you have to reference the weapon against a master list. This is actually how Destiny Item Manager works and requires updating of a manifest with each weapon update.

My point is, while it would be possible, through enough shenanigans to figure out which weapons you had were armsday orders and remind you, it wouldn't be any fun to create and would require more work and maintenance than it's really worth which is probably why it doesn't exist already. Which leads me to tell you, add something to your calendar like Earendil suggested.

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