To encourage my writing habit, I've made a wager with a group of friends:

Each person involved in the wager chooses a charity (the charities must be something that none of the others have chosen nor can any of the others find the charity immoral). Each person agrees to start work on a large project (in this case, novels). When one of us completes their project, they donate a set amount of money to the charity of their choice. If anyone gives up or goes a set amount of time (in this case, a month) without progress on the project, they instead donate to the other charities.

I fashioned the wager this way to encourage dedication to the project without emphasizing speed or competition. We're working on novels, so encouraging people to rush would only make their writing sloppy and destroy the joy of the work. The month time limit is, I feel, longer than needed, but will serve the purpose of keeping us checking on each other and encouraging each other. The charities were chosen so that money would not become a sticking point. No one gains personally, but there is no feeling of being cheated out of cash. A donation will be made no matter what, and since the charities must be such that no player feels them to be immoral, those donations will have some level of good feelings attached. Meaning no one walks away sour.