The Challenge for January is Jumping Lunges!
Do a quantity of jumping lunges that equals 5 times the date (5 jumping lunges on Jan 1st, 10 jumping lunges on Jan 2nd, etc.).
Remember to start down on a knee, jumping and switching knees = 1 rep. (Yes, this means that on odd numbered days, you will end up doing one more rep on one side than the other. If you want to be even from side to side, change which knee you start with!) Stay tall, try not to land the front foot before the back one.