If you are looking for a little extra challenge this month, consider playing Advent of Code. A pair of holiday themed problems are presented daily, December 1-25. I'm not trying to steer people from CheckiO; I'm just sharing another option available for the next three weeks.
I'm not affiliated with this site, and honestly can only answer the first few problems presented! :)
Good luck & have fun!
http://adventofcode.com/2016
Created at: Dec. 6, 2016, 6:24 p.m.; Updated at: Dec. 8, 2016, 7:31 p.m.