AKA: The Regifting of the White Elephants
Note - I'm not sure this is on-topic or not on meta, but it seems to be as good a place as any. Comment if you disagree.
I have a few challenges that I have posted to the sandbox and then more-or-less forgotten. Some of these challenges are OK; some not so much. I think all of them could do with at least some level of polishing before they are posted to main.
So this is my christmas gift to the community this year. I don't think I have the inclination to pick up any of these challenges right now, if ever, so if you are interested, you may claim ownership and run with it.
I will post the challenges I am donating as answers to this question. If you have similar challenges you wish to donate, then please feel free to post as answers too.
If you are interested in picking up any of these, go ahead and indicate this in the comments.
Up/down-vote answers to indicate your interest solving a challenge. This will give potential new owners a feel for whether its worth picking up that challenge.
If you are taking one of these challenge ideas, you should either edit the existing sandbox entry with your ideas, or perhaps create a new sandbox entry.