Collaboration software company Huddle is running a special holiday promotion. Users who upgrade from a free subscription to a premium account by the end of December will get one month free and a chance to win $250 in Amazon.com vouchers. One in every ten subscribers will win, according to an announcement on Huddle's website.

Originally, Huddle was offering a Kindle to winners of the contest, but switched the prize after receiving a "flurry of user feedback demanding an alternative," according to the announcement.

Huddle's paid subscriptions start at $15 a month for five online workspaces with project and collaboration tools and 2.5 GB of storage.