what's the deal with Bach's bwv1079 and 1080

[samthegreat]

bwv1079 - The Musical Offering
bwv1080 - The Art of the Fugue

I organize all my sheet music pdfs pretty explicitly. Every work I have, at the end of the filename I put the applicable instrument(s) in parentheses, except for solo piano. (no parentheses with instrument implies solo piano). I am having trouble figuring out the exact purposes of these two Bach works - are they studies, etc. or can they be played by multiple instruments? I'm not really sure what the point of these works are. Can someone help with some insight?