What programmers should do if there are no tasks in hand for few days? [duplicate]

Question

Possible Duplicate:
How to productively spend “free time” at the office

Sometimes specially in the end of the year in software companies, there are less work for the team, at least this happen in my company.

What should I ask my developers team to do during these cold days?

What things they can do which can keep them focused and that will improve the company in next year and future?